erlang

MODULE

erlang

MODULE SUMMARY

The Erlang BIFs

DESCRIPTION

By convention, most built-in functions (BIFs) are seen as being
in the module erlang. A number of the BIFs are viewed more
or less as part of the Erlang programming language and are
auto-imported. Thus, it is not necessary to specify
the module name and both the calls atom_to_list(Erlang) and
erlang:atom_to_list(Erlang) are identical.

In the text, auto-imported BIFs are listed without module prefix.
BIFs listed with module prefix are not auto-imported.

BIFs may fail for a variety of reasons. All BIFs fail with
reason badarg if they are called with arguments of an
incorrect type. The other reasons that may make BIFs fail are
described in connection with the description of each individual
BIF.

Some BIFs may be used in guard tests, these are marked with
"Allowed in guard tests".

Returns a new tuple which has one element more than
Tuple1, and contains the elements in Tuple1
followed by Term as the last element. Semantically
equivalent to
list_to_tuple(tuple_to_list(Tuple1) ++ [Term]), but much
faster.

> erlang:append_element({one, two}, three).
{one,two,three}

apply(Fun, Args) -> term()

Types:

Fun = function()

Args = [term()]

Call a fun, passing the elements in Args as
arguments.

Note: If the number of elements in the arguments are known at
compile-time, the call is better written as
Fun(Arg1, Arg2, ... ArgN).

Warning

Earlier, Fun could also be given as
{Module, Function}, equivalent to
apply(Module, Function, Args). This usage is
deprecated and will stop working in a future release of
Erlang/OTP.

apply(Module, Function, Args) -> term()

Types:

Module = module()

Function = atom()

Args = [term()]

Returns the result of applying Function in
Module to Args. The applied function must
be exported from Module. The arity of the function is
the length of Args.

> apply(lists, reverse, [[a, b, c]]).
[c,b,a]

apply can be used to evaluate BIFs by using
the module name erlang.

> apply(erlang, atom_to_list, ['Erlang']).
"Erlang"

Note: If the number of arguments are known at compile-time,
the call is better written as
Module:Function(Arg1, Arg2, ..., ArgN).

Failure: error_handler:undefined_function/3 is called
if the applied function is not exported. The error handler
can be redefined (see
process_flag/2).
If the error_handler is undefined, or if the user has
redefined the default error_handler so the replacement
module is undefined, an error with the reason undef
is generated.

atom_to_binary(Atom, Encoding) -> binary()

Types:

Atom = atom()

Encoding = latin1 | unicode | utf8

Returns a binary which corresponds to the text
representation of Atom. If Encoding
is latin1, there will be one byte for each character
in the text representation. If Encoding is
utf8 or
unicode, the characters will be encoded using UTF-8
(meaning that characters from 16#80 up to 0xFF will be
encoded in two bytes).

Note

Currently, atom_to_binary(Atom, latin1) can
never fail because the text representation of an atom can only contain
characters from 0 to 16#FF. In a future release, the text representation
of atoms might be allowed to contain any Unicode character
and atom_to_binary(Atom, latin1) will fail if the
text representation for the Atom contains a Unicode
character greater than 16#FF.

> atom_to_binary('Erlang', latin1).
<<"Erlang">>

atom_to_list(Atom) -> string()

Types:

Atom = atom()

Returns a string which corresponds to the text
representation of Atom.

If PosLen in any way references outside the binary, a badarg exception is raised.

Start is zero-based, i.e.:

1> Bin = <<1,2,3>>
2> binary_part(Bin,{0,2}).
<<1,2>>

See the STDLIB module binary for details about the PosLen semantics.

Allowed in guard tests.

binary_part(Subject, Start, Length) -> binary()

Types:

Subject = binary()

Start = integer() >= 0

Length = integer()

The same as binary_part(Subject, {Start, Length}).

Allowed in guard tests.

binary_to_atom(Binary, Encoding) -> atom()

Types:

Binary = binary()

Encoding = latin1 | unicode | utf8

Returns the atom whose text representation is
Binary. If Encoding is latin1, no
translation of bytes in the binary is done. If Encoding
is utf8 or unicode, the binary must contain
valid UTF-8 sequences; furthermore, only Unicode characters up
to 0xFF are allowed.

Note

binary_to_atom(Binary, utf8) will fail if
the binary contains Unicode characters greater than 16#FF.
In a future release, such Unicode characters might be allowed
and binary_to_atom(Binary, utf8)
will not fail in that case. For more information on Unicode support in atoms
see note on UTF-8 encoded atoms
in the chapter about the external term format in the ERTS User's Guide.

Failure: badarg if Binary contains a bad
representation of an integer.

binary_to_integer(Binary, Base) -> integer()

Types:

Binary = binary()

Base = 2..36

Returns an integer whose text representation in base
Base is Binary.

> binary_to_integer(<<"3FF">>, 16).
1023

Failure: badarg if Binary contains a bad
representation of an integer.

binary_to_list(Binary) -> [byte()]

Types:

Binary = binary()

Returns a list of integers which correspond to the bytes of
Binary.

binary_to_list(Binary, Start, Stop) -> [byte()]

Types:

Binary = binary()

Start = Stop = integer() >= 1

1..byte_size(Binary)

As binary_to_list/1, but returns a list of integers
corresponding to the bytes from position Start to
position Stop in Binary. Positions in the
binary are numbered starting from 1.

Note

This function's indexing style of using one-based indices for
binaries is deprecated. New code should use the functions in
the STDLIB module binary instead. They consequently
use the same (zero-based) style of indexing.

bitstring_to_list(Bitstring) -> [byte() | bitstring()]

Types:

Bitstring = bitstring()

Returns a list of integers which correspond to the bytes of
Bitstring. If the number of bits in the binary is not
divisible by 8, the last element of the list will be a bitstring
containing the remaining bits (1 up to 7 bits).

As binary_to_term/1, but takes options that affect decoding
of the binary.

safe

Use this option when receiving binaries from an untrusted
source.

When enabled, it prevents decoding data that may be used to
attack the Erlang system. In the event of receiving unsafe
data, decoding fails with a badarg error.

Currently, this prevents creation of new atoms directly,
creation of new atoms indirectly (as they are embedded in
certain structures like pids, refs, funs, etc.), and creation of
new external function references. None of those resources are
currently garbage collected, so unchecked creation of them can
exhaust available memory.

This implementation-dependent function increments
the reduction counter for the calling process. In the Beam
emulator, the reduction counter is normally incremented by
one for each function and BIF call, and a context switch is
forced when the counter reaches the maximum number of reductions
for a process (2000 reductions in R12B).

Warning

This BIF might be removed in a future version of the Beam
machine without prior warning. It is unlikely to be
implemented in other Erlang implementations.

byte_size(Bitstring) -> integer() >= 0

Types:

Bitstring = bitstring()

Returns an integer which is the number of bytes needed to contain
Bitstring. (That is, if the number of bits in Bitstring is not
divisible by 8, the resulting number of bytes will be rounded up.)

> byte_size(<<433:16,3:3>>).
3
> byte_size(<<1,2,3>>).
3

Allowed in guard tests.

erlang:cancel_timer(TimerRef) -> Time | false

Types:

TimerRef = reference()

Time = integer() >= 0

Cancels a timer, where TimerRef was returned by
either
erlang:send_after/3
or
erlang:start_timer/3.
If the timer is there to be removed, the function returns
the time in milliseconds left until the timer would have expired,
otherwise false (which means that TimerRef was
never a timer, that it has already been cancelled, or that it
has already delivered its message).

Returns true if the process Pid is executing
old code for Module. That is, if the current call of
the process executes old code for this module, or if the
process has references to old code for this module, or if the
process contains funs that references old code for this
module. Otherwise, it returns false.

Decodes the binary Bin according to the packet
protocol specified by Type. Very similar to the packet
handling done by sockets with the option {packet,Type}.

If an entire packet is contained in Bin it is
returned together with the remainder of the binary as
{ok,Packet,Rest}.

If Bin does not contain the entire packet,
{more,Length} is returned. Length is either the
expected total size of the packet or undefined
if the expected packet size is not known. decode_packet
can then be called again with more data added.

If the packet does not conform to the protocol format
{error,Reason} is returned.

The following values of Type are valid:

raw | 0

No packet handling is done. Entire binary is
returned unless it is empty.

1 | 2 | 4

Packets consist of a header specifying the number of
bytes in the packet, followed by that number of bytes.
The length of header can be one, two, or four bytes;
the order of the bytes is big-endian. The header
will be stripped off when the packet is returned.

line

A packet is a line terminated with newline. The
newline character is included in the returned packet
unless the line was truncated according to the option
line_length.

asn1 | cdr | sunrm | fcgi | tpkt

The header is not stripped off.

The meanings of the packet types are as follows:

asn1 - ASN.1 BER

sunrm - Sun's RPC encoding

cdr - CORBA (GIOP 1.1)

fcgi - Fast CGI

tpkt - TPKT format [RFC1006]

http | httph | http_bin | httph_bin

The Hypertext Transfer Protocol. The packets
are returned with the format according to
HttpPacket described above. A packet is either a
request, a response, a header or an end of header
mark. Invalid lines are returned as HttpError.

Recognized request methods and header fields are returned as atoms.
Others are returned as strings. Strings of unrecognized header fields
are formatted with only capital letters first and after hyphen characters
(like "Sec-Websocket-Key").

The protocol type http should only be used for
the first line when a HttpRequest or a
HttpResponse is expected. The following calls
should use httph to get HttpHeader's until
http_eoh is returned that marks the end of the
headers and the beginning of any following message body.

The variants http_bin and httph_bin will return
strings (HttpString) as binaries instead of lists.

The following options are available:

{packet_size, integer() >= 0}

Sets the max allowed size of the packet body. If
the packet header indicates that the length of the
packet is longer than the max allowed length, the packet
is considered invalid. Default is 0 which means no
size limit.

Makes the current code for Module become old code, and
deletes all references for this module from the export table.
Returns undefined if the module does not exist,
otherwise true.

Warning

This BIF is intended for the code server (see
code(3)) and should not be
used elsewhere.

Failure: badarg if there is already an old version of
Module.

demonitor(MonitorRef) -> true

Types:

MonitorRef = reference()

If MonitorRef is a reference which the calling process
obtained by calling
monitor/2,
this monitoring is turned off. If the monitoring is already
turned off, nothing happens.

Once demonitor(MonitorRef) has returned it is
guaranteed that no {'DOWN', MonitorRef, _, _, _} message
due to the monitor will be placed in the caller's message queue
in the future. A {'DOWN', MonitorRef, _, _, _} message
might have been placed in the caller's message queue prior to
the call, though. Therefore, in most cases, it is advisable
to remove such a 'DOWN' message from the message queue
after monitoring has been stopped.
demonitor(MonitorRef, [flush]) can be used instead of
demonitor(MonitorRef) if this cleanup is wanted.

Note

Prior to OTP release R11B (erts version 5.5) demonitor/1
behaved completely asynchronous, i.e., the monitor was active
until the "demonitor signal" reached the monitored entity. This
had one undesirable effect, though. You could never know when
you were guaranteed not to receive a DOWN message
due to the monitor.

Current behavior can be viewed as two combined operations:
asynchronously send a "demonitor signal" to the monitored entity
and ignore any future results of the monitor.

Failure: It is an error if MonitorRef refers to a
monitoring started by another process. Not all such cases are
cheap to check; if checking is cheap, the call fails with
badarg (for example if MonitorRef is a remote
reference).

The monitor was found and removed. In this case
no 'DOWN' message due to this monitor have
been nor will be placed in the message queue
of the caller.

false

The monitor was not found and could not be removed.
This probably because someone already has placed a
'DOWN' message corresponding to this monitor
in the caller's message queue.

If the info option is combined with the flush
option, false will be returned if a flush was needed;
otherwise, true.

Note

More options may be added in the future.

Failure: badarg if OptionList is not a list, or
if Option is not a valid option, or the same failure as for
demonitor/1

disconnect_node(Node) -> boolean() | ignored

Types:

Node = node()

Forces the disconnection of a node. This will appear to
the node Node as if the local node has crashed. This
BIF is mainly used in the Erlang network authentication
protocols. Returns true if disconnection succeeds,
otherwise false. If the local node is not alive,
the function returns ignored.

Stops the execution of the calling process with the reason
Reason, where Reason is any term. The actual
exit reason will be {Reason, Where}, where Where
is a list of the functions most recently called (the current
function first). Since evaluating this function causes
the process to terminate, it has no return value.

Stops the execution of the calling process with the reason
Reason, where Reason is any term. The actual
exit reason will be {Reason, Where}, where Where
is a list of the functions most recently called (the current
function first). Args is expected to be the list of
arguments for the current function; in Beam it will be used
to provide the actual arguments for the current function in
the Where term. Since evaluating this function causes
the process to terminate, it has no return value.

exit(Reason) -> no_return()

Types:

Reason = term()

Stops the execution of the calling process with the exit
reason Reason, where Reason is any term. Since
evaluating this function causes the process to terminate, it
has no return value.

Sends an exit signal with exit reason Reason to
the process or port identified by Pid.

The following behavior apply if Reason is any term
except normal or kill:

If Pid is not trapping exits, Pid itself will
exit with exit reason Reason. If Pid is trapping
exits, the exit signal is transformed into a message
{'EXIT', From, Reason} and delivered to the message
queue of Pid. From is the pid of the process
which sent the exit signal. See also
process_flag/2.

If Reason is the atom normal, Pid will
not exit. If it is trapping exits, the exit signal is
transformed into a message {'EXIT', From, normal}
and delivered to its message queue.

If Reason is the atom kill, that is if
exit(Pid, kill) is called, an untrappable exit signal
is sent to Pid which will unconditionally exit with
exit reason killed.

erlang:external_size(Term) -> integer() >= 0

Types:

Term = term()

Calculates, without doing the encoding, the maximum byte size for
a term encoded in the Erlang external term format. The following
condition applies always:

Returns a string which corresponds to the text
representation of Float using fixed decimal point formatting.
When decimals option is specified
the returned value will contain at most Decimals number of
digits past the decimal point. If the number doesn't fit in the
internal static buffer of 256 bytes, the function throws badarg.
When compact option is provided
the trailing zeros at the end of the list are truncated (this option is
only meaningful together with the decimals option). When
scientific option is provided, the float will be formatted using
scientific notation with Decimals digits of precision. If
Options is [] the function behaves like
float_to_list/1.

Returns a list containing information about the fun
Fun. Each element of the list is a tuple. The order of
the tuples is not defined, and more tuples may be added in a
future release.

Warning

This BIF is mainly intended for debugging, but it can
occasionally be useful in library functions that might need
to verify, for instance, the arity of a fun.

There are two types of funs with slightly different
semantics:

A fun created by fun M:F/A is called an
external fun. Calling it will always call the
function F with arity A in the latest code for
module M. Note that module M does not even need
to be loaded when the fun fun M:F/A is created.

All other funs are called local. When a local fun
is called, the same version of the code that created the fun
will be called (even if newer version of the module has been
loaded).

The following elements will always be present in the list
for both local and external funs:

{type, Type}

Type is either local or external.

{module, Module}

Module (an atom) is the module name.

If Fun is a local fun, Module is the module
in which the fun is defined.

If Fun is an external fun, Module is the
module that the fun refers to.

{name, Name}

Name (an atom) is a function name.

If Fun is a local fun, Name is the name
of the local function that implements the fun.
(This name was generated by the compiler, and is generally
only of informational use. As it is a local function, it
is not possible to call it directly.)
If no code is currently loaded for the fun, []
will be returned instead of an atom.

If Fun is an external fun, Name is the name
of the exported function that the fun refers to.

{arity, Arity}

Arity is the number of arguments that the fun
should be called with.

{env, Env}

Env (a list) is the environment or free variables
for the fun. (For external funs, the returned list is
always empty.)

The following elements will only be present in the list if
Fun is local:

{pid, Pid}

Pid is the pid of the process that originally
created the fun.

{index, Index}

Index (an integer) is an index into the module's
fun table.

{new_index, Index}

Index (an integer) is an index into the module's
fun table.

{new_uniq, Uniq}

Uniq (a binary) is a unique value for this fun.
It is calculated from the compiled code for the entire module.

{uniq, Uniq}

Uniq (an integer) is a unique value for this fun.
Starting in the R15 release, this integer is calculated from
the compiled code for the entire module. Before R15, this
integer was based on only the body of the fun.

Returns true if the module Module is loaded
and contains an exported function Function/Arity;
otherwise false.

Returns false for any BIF (functions implemented in C
rather than in Erlang).

garbage_collect() -> true

Forces an immediate garbage collection of the currently
executing process. The function should not be used, unless
it has been noticed -- or there are good reasons to suspect --
that the spontaneous garbage collection will occur too late
or not at all. Improper use may seriously degrade system
performance.

Compatibility note: In versions of OTP prior to R7,
the garbage collection took place at the next context switch,
not immediately. To force a context switch after a call to
erlang:garbage_collect(), it was sufficient to make
any function call.

garbage_collect(Pid) -> boolean()

Types:

Pid = pid()

Works like erlang:garbage_collect() but on any
process. The same caveats apply. Returns false if
Pid refers to a dead process; true otherwise.

Get the call stack back-trace (stacktrace) of the last
exception in the calling process as a list of
{Module,Function,Arity,Location} tuples.
The Arity field in the first tuple may be the argument
list of that function call instead of an arity integer,
depending on the exception.

If there has not been any exceptions in a process, the
stacktrace is []. After a code change for the process,
the stacktrace may also be reset to [].

The stacktrace is the same data as the catch operator
returns, for example:

{'EXIT',{badarg,Stacktrace}} = catch abs(x)

Location is a (possibly empty) list of two-tuples that
may indicate the location in the source code of the function.
The first element is an atom that describes the type of
information in the second element. Currently the following
items may occur:

file

The second element of the tuple is a string (list of
characters) representing the filename of the source file
of the function.

line

The second element of the tuple is the line number
(an integer greater than zero) in the source file
where the exception occurred or the function was called.

Returns the pid of the group leader for the process which
evaluates the function.

Every process is a member of some process group and all
groups have a group leader. All IO from the group
is channeled to the group leader. When a new process is
spawned, it gets the same group leader as the spawning
process. Initially, at system start-up, init is both
its own group leader and the group leader of all processes.

group_leader(GroupLeader, Pid) -> true

Types:

GroupLeader = Pid = pid()

Sets the group leader of Pid to GroupLeader.
Typically, this is used when a processes started from a
certain shell should have another group leader than
init.

Status must be a non-negative integer, a string,
or the atom abort.
Halts the Erlang runtime system. Has no return value.
Depending on Status:

integer()

The runtime system exits with the integer value Status
as status code to the calling environment (operating system).

string()

An erlang crash dump is produced with Status as slogan,
and then the runtime system exits with status code 1.

abort

The runtime system aborts producing a core dump, if that is
enabled in the operating system.

Note that on many platforms, only the status codes 0-255 are
supported by the operating system.

For integer Status the Erlang runtime system closes all ports
and allows async threads to finish their operations before exiting.
To exit without such flushing use
Option as {flush,false}.

For statuses string() and abort the flush
option is ignored and flushing is not done.

erlang:hash(Term, Range) -> integer() >= 1

Types:

Term = term()

Range = integer() >= 1

Returns a hash value for Term within the range
1..Range. The allowed range is 1..2^27-1.

Warning

This BIF is deprecated as the hash value may differ on
different architectures. Also the hash values for integer
terms larger than 2^27 as well as large binaries are very
poor. The BIF is retained for backward compatibility
reasons (it may have been used to hash records into a file),
but all new code should use one of the BIFs
erlang:phash/2 or erlang:phash2/1,2 instead.

hd(List) -> term()

Types:

List = [term(), ...]

Returns the head of List, that is, the first element.

> hd([1,2,3,4,5]).
1

Allowed in guard tests.

Failure: badarg if List is the empty list [].

erlang:hibernate(Module, Function, Args) -> no_return()

Types:

Module = module()

Function = atom()

Args = [term()]

Puts the calling process into a wait state where its memory
allocation has been reduced as much as possible, which is
useful if the process does not expect to receive any messages
in the near future.

The process will be awaken when a message is sent to it, and
control will resume in Module:Function with
the arguments given by Args with the call stack
emptied, meaning that the process will terminate when that
function returns. Thus erlang:hibernate/3 will never
return to its caller.

If the process has any message in its message queue,
the process will be awaken immediately in the same way as
described above.

In more technical terms, what erlang:hibernate/3 does
is the following. It discards the call stack for the process.
Then it garbage collects the process. After the garbage
collection, all live data is in one continuous heap. The heap
is then shrunken to the exact same size as the live data
which it holds (even if that size is less than the minimum
heap size for the process).

If the size of the live data in the process is less than
the minimum heap size, the first garbage collection occurring
after the process has been awaken will ensure that the heap
size is changed to a size not smaller than the minimum heap
size.

Note that emptying the call stack means that any surrounding
catch is removed and has to be re-inserted after
hibernation. One effect of this is that processes started
using proc_lib (also indirectly, such as
gen_server processes), should use
proc_lib:hibernate/3
instead to ensure that the exception handler continues to work
when the process wakes up.

erlang:insert_element(Index, Tuple1, Term) -> Tuple2

Types:

Index = integer() >= 1

1..tuple_size(Tuple1) + 1

Tuple1 = Tuple2 = tuple()

Term = term()

Returns a new tuple with element Term insert at position
Index in tuple Tuple1.
All elements from position Index and upwards are subsequently
pushed one step higher in the new tuple Tuple2.

Returns an integer which is the size in bytes
of the binary that would be the result of
iolist_to_binary(Item).

> iolist_size([1,2|<<3,4>>]).
4

is_alive() -> boolean()

Returns true if the local node is alive; that is, if
the node can be part of a distributed system. Otherwise, it
returns false.

is_atom(Term) -> boolean()

Types:

Term = term()

Returns true if Term is an atom;
otherwise returns false.

Allowed in guard tests.

is_binary(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a binary;
otherwise returns false.

A binary always contains a complete number of bytes.

Allowed in guard tests.

is_bitstring(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a bitstring (including a binary);
otherwise returns false.

Allowed in guard tests.

is_boolean(Term) -> boolean()

Types:

Term = term()

Returns true if Term is
either the atom true or the atom false
(i.e. a boolean); otherwise returns false.

Allowed in guard tests.

erlang:is_builtin(Module, Function, Arity) -> boolean()

Types:

Module = module()

Function = atom()

Arity = arity()

Returns true if Module:Function/Arity is
a BIF implemented in C; otherwise returns false.
This BIF is useful for builders of cross reference tools.

is_float(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a floating point
number; otherwise returns false.

Allowed in guard tests.

is_function(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a fun; otherwise
returns false.

Allowed in guard tests.

is_function(Term, Arity) -> boolean()

Types:

Term = term()

Arity = arity()

Returns true if Term is a fun that can be
applied with Arity number of arguments; otherwise
returns false.

Allowed in guard tests.

is_integer(Term) -> boolean()

Types:

Term = term()

Returns true if Term is an integer;
otherwise returns false.

Allowed in guard tests.

is_list(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a list with
zero or more elements; otherwise returns false.

Allowed in guard tests.

is_number(Term) -> boolean()

Types:

Term = term()

Returns true if Term is either an integer or a
floating point number; otherwise returns false.

Allowed in guard tests.

is_pid(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a pid (process
identifier); otherwise returns false.

Allowed in guard tests.

is_port(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a port identifier;
otherwise returns false.

Allowed in guard tests.

is_process_alive(Pid) -> boolean()

Types:

Pid = pid()

Pid must refer to a process at the local node.
Returns true if the process exists and is alive, that
is, is not exiting and has not exited. Otherwise, returns
false.

is_record(Term, RecordTag) -> boolean()

Types:

Term = term()

RecordTag = atom()

Returns true if Term is a tuple and its first
element is RecordTag. Otherwise, returns false.

Note

Normally the compiler treats calls to is_record/2
specially. It emits code to verify that Term is a
tuple, that its first element is RecordTag, and that
the size is correct. However, if the RecordTag is
not a literal atom, the is_record/2 BIF will be
called instead and the size of the tuple will not be
verified.

Allowed in guard tests, if RecordTag is a literal
atom.

is_record(Term, RecordTag, Size) -> boolean()

Types:

Term = term()

RecordTag = atom()

Size = integer() >= 0

RecordTag must be an atom. Returns true if
Term is a tuple, its first element is RecordTag,
and its size is Size. Otherwise, returns false.

Allowed in guard tests, provided that RecordTag is
a literal atom and Size is a literal integer.

Note

This BIF is documented for completeness. In most cases
is_record/2 should be used.

is_reference(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a reference;
otherwise returns false.

Allowed in guard tests.

is_tuple(Term) -> boolean()

Types:

Term = term()

Returns true if Term is a tuple;
otherwise returns false.

Allowed in guard tests.

length(List) -> integer() >= 0

Types:

List = [term()]

Returns the length of List.

> length([1,2,3,4,5,6,7,8,9]).
9

Allowed in guard tests.

link(PidOrPort) -> true

Types:

PidOrPort = pid() | port()

Creates a link between the calling process and another
process (or port) PidOrPort, if there is not such a link
already. If a process attempts to create a link to itself,
nothing is done. Returns true.

If PidOrPort does not exist, the behavior of the BIF depends
on if the calling process is trapping exits or not (see
process_flag/2):

If the calling process is not trapping exits, and
checking PidOrPort is cheap -- that is, if PidOrPort is
local -- link/1 fails with reason noproc.

Otherwise, if the calling process is trapping exits,
and/or PidOrPort is remote, link/1 returns
true, but an exit signal with reason noproc
is sent to the calling process.

list_to_atom(String) -> atom()

Types:

String = string()

Returns the atom whose text representation is String.

String may only contain ISO-latin-1
characters (i.e. numbers below 256) as the current
implementation does not allow unicode characters >= 256 in
atoms. For more information on Unicode support in atoms
see note on UTF-8 encoded atoms
in the chapter about the external term format in the ERTS User's Guide.

> list_to_atom("Erlang").
'Erlang'

list_to_binary(IoList) -> binary()

Types:

IoList = iolist()

Returns a binary which is made from the integers and
binaries in IoList.

If Binary contains the object code for the module
Module, this BIF loads that object code. Also, if
the code for the module Module already exists, all
export references are replaced so they point to the newly
loaded code. The previously loaded code is kept in the system
as old code, as there may still be processes which are
executing that code. It returns either
{module, Module}, or {error, Reason} if loading
fails. Reason is one of the following:

badfile

The object code in Binary has an
incorrect format or the object code contains code
for another module than Module.

not_purged

Binary contains a module which cannot be loaded
because old code for this module already exists.

Warning

This BIF is intended for the code server (see
code(3)) and should not be
used elsewhere.

erlang:load_nif(Path, LoadInfo) -> ok | Error

Types:

Path = string()

LoadInfo = term()

Error = {error, {Reason, Text :: string()}}

Reason = load_failed | bad_lib | load | reload | upgrade | old_code

Note

In releases older than OTP R14B, NIFs were an
experimental feature. Versions of OTP older than R14B might
have different and possibly incompatible NIF semantics and
interfaces. For example, in R13B03 the return value on
failure was
{error,Reason,Text}.

Loads and links a dynamic library containing native
implemented functions (NIFs) for a module. Path is a
file path to the sharable object/dynamic library file minus
the OS-dependent file extension (.so for Unix and .dll for
Windows). See erl_nif
on how to implement a NIF library.

LoadInfo can be any term. It will be passed on to
the library as part of the initialization. A good practice is
to include a module version number to support future code
upgrade scenarios.

The call to load_nif/2 must be made
directly from the Erlang code of the module that the
NIF library belongs to.

It returns either ok, or {error,{Reason,Text}}
if loading fails. Reason is one of the atoms below,
while Text is a human readable string that may give
some more information about the failure.

load_failed

The OS failed to load the NIF library.

bad_lib

The library did not fulfil the requirements as a NIF
library of the calling module.

load | reload | upgrade

The corresponding library callback was not successful.

old_code

The call to load_nif/2 was made from the old
code of a module that has been upgraded. This is not
allowed.

erlang:loaded() -> [Module]

Types:

Module = module()

Returns a list of all loaded Erlang modules (current and/or
old code), including preloaded modules.

Converts local date and time to Universal Time Coordinated
(UTC) just like erlang:localtime_to_universaltime/1,
but the caller decides if daylight saving time is active or
not.

If IsDst == true the Localtime is during
daylight saving time, if IsDst == false it is not,
and if IsDst == undefined the underlying OS may
guess, which is the same as calling
erlang:localtime_to_universaltime(Localtime).

The returned reference will re-occur after approximately 2^82
calls; therefore it is unique enough for practical purposes.

> make_ref().
#Ref<0.0.0.135>

erlang:make_tuple(Arity, InitialValue) -> tuple()

Types:

Arity = arity()

InitialValue = term()

Returns a new tuple of the given Arity, where all
elements are InitialValue.

> erlang:make_tuple(4, []).
{[],[],[],[]}

erlang:make_tuple(Arity, DefaultValue, InitList) -> tuple()

Types:

Arity = arity()

DefaultValue = term()

InitList = [{Position :: integer() >= 1, term()}]

erlang:make_tuple first creates a tuple of size Arity
where each element has the value DefaultValue. It then fills
in values from InitList. Each list element in InitList
must be a two-tuple where the first element is a position in the
newly created tuple and the second element is any term. If a position
occurs more than once in the list, the term corresponding to
last occurrence will be used.

Returns a list containing information about memory
dynamically allocated by the Erlang emulator. Each element of
the list is a tuple {Type, Size}. The first element
Typeis an atom describing memory type. The second
element Sizeis memory size in bytes. A description of
each memory type follows:

total

The total amount of memory currently allocated, which is
the same as the sum of memory size for processes
and system.

processes

The total amount of memory currently allocated by
the Erlang processes.

processes_used

The total amount of memory currently used by the Erlang
processes.

This memory is part of the memory presented as
processes memory.

system

The total amount of memory currently allocated by
the emulator that is not directly related to any Erlang
process.

Memory presented as processes is not included in
this memory.

atom

The total amount of memory currently allocated for atoms.

This memory is part of the memory presented as
system memory.

atom_used

The total amount of memory currently used for atoms.

This memory is part of the memory presented as
atom memory.

binary

The total amount of memory currently allocated for
binaries.

This memory is part of the memory presented as
system memory.

code

The total amount of memory currently allocated for
Erlang code.

This memory is part of the memory presented as
system memory.

ets

The total amount of memory currently allocated for ets
tables.

This memory is part of the memory presented as
system memory.

low

Only on 64-bit halfword emulator.

The total amount of memory allocated in low memory areas
that are restricted to less than 4 Gb even though
the system may have more physical memory.

May be removed in future releases of halfword emulator.

maximum

The maximum total amount of memory allocated since
the emulator was started.

This tuple is only present when the emulator is run with
instrumentation.

For information on how to run the emulator with
instrumentation see
instrument(3)
and/or erl(1).

Note

The system value is not complete. Some allocated
memory that should be part of the system value are
not.

When the emulator is run with instrumentation,
the system value is more accurate, but memory
directly allocated by malloc (and friends) are still
not part of the system value. Direct calls to
malloc are only done from OS specific runtime
libraries and perhaps from user implemented Erlang drivers
that do not use the memory allocation functions in
the driver interface.

Since the total value is the sum of processes
and system the error in system will propagate
to the total value.

The different amounts of memory that are summed are
not gathered atomically which also introduce
an error in the result.

The different values has the following relation to each
other. Values beginning with an uppercase letter is not part
of the result.

The total value is supposed to be the total amount
of memory dynamically allocated by the emulator. Shared
libraries, the code of the emulator itself, and
the emulator stack(s) are not supposed to be included. That
is, the total value is not supposed to be
equal to the total size of all pages mapped to the emulator.
Furthermore, due to fragmentation and pre-reservation of
memory areas, the size of the memory segments which contain
the dynamically allocated memory blocks can be substantially
larger than the total size of the dynamically allocated
memory blocks.

Note

Since erts version 5.6.4 erlang:memory/0 requires that
all erts_alloc(3)
allocators are enabled (default behaviour).

Returns the memory size in bytes allocated for memory of
type Type. The argument can also be given as a list
of memory_type() atoms, in which case a corresponding list of
{memory_type(), Size :: integer >= 0} tuples is returned.

Note

Since erts version 5.6.4 erlang:memory/1 requires that
all erts_alloc(3)
allocators are enabled (default behaviour).

Failures:

badarg

If Type is not one of the memory types listed in the
documentation of
erlang:memory/0.

badarg

If maximum is passed as Type and the emulator
is not run in instrumented mode.

Return the smallest of Term1 and Term2;
if the terms compare equal, Term1 will be returned.

module_loaded(Module) -> boolean()

Types:

Module = module()

Returns true if the module Module is loaded,
otherwise returns false. It does not attempt to load
the module.

Warning

This BIF is intended for the code server (see
code(3)) and should not be
used elsewhere.

monitor(Type, Item) -> MonitorRef

Types:

Type = process

Item = pid() | Module | {Module, Node}

Module = module()

Node = node()

MonitorRef = reference()

The calling process starts monitoring Item which is
an object of type Type.

Currently only processes can be monitored, i.e. the only
allowed Type is process, but other types may be
allowed in the future.

Item can be:

pid()

The pid of the process to monitor.

{RegName, Node}

A tuple consisting of a registered name of a process and
a node name. The process residing on the node Node
with the registered name RegName will be monitored.

RegName

The process locally registered as RegName will be
monitored.

Note

When a process is monitored by registered name, the process
that has the registered name at the time when
monitor/2 is called will be monitored.
The monitor will not be effected, if the registered name is
unregistered.

A 'DOWN' message will be sent to the monitoring
process if Item dies, if Item does not exist,
or if the connection is lost to the node which Item
resides on. A 'DOWN' message has the following pattern:

{'DOWN', MonitorRef, Type, Object, Info}

where MonitorRef and Type are the same as
described above, and:

Object

A reference to the monitored object:

the pid of the monitored process, if Item was
specified as a pid.

{RegName, Node}, if Item was specified as
{RegName, Node}.

{RegName, Node}, if Item was specified as
RegName. Node will in this case be the
name of the local node (node()).

Info

Either the exit reason of the process, noproc
(non-existing process), or noconnection (no
connection to Node).

Note

If/when monitor/2 is extended (e.g. to
handle other item types than process), other
possible values for Object, and Info in the
'DOWN' message will be introduced.

The monitoring is turned off either when the 'DOWN'
message is sent, or when
demonitor/1
is called.

If an attempt is made to monitor a process on an older node
(where remote process monitoring is not implemented or one
where remote process monitoring by registered name is not
implemented), the call fails with badarg.

Making several calls to monitor/2 for the same
Item is not an error; it results in as many, completely
independent, monitorings.

Note

The format of the 'DOWN' message changed in the 5.2
version of the emulator (OTP release R9B) for monitor by registered name. The Object element of
the 'DOWN' message could in earlier versions
sometimes be the pid of the monitored process and sometimes
be the registered name. Now the Object element is
always a tuple consisting of the registered name and
the node name. Processes on new nodes (emulator version 5.2
or greater) will always get 'DOWN' messages on
the new format even if they are monitoring processes on old
nodes. Processes on old nodes will always get 'DOWN'
messages on the old format.

monitor_node(Node, Flag) -> true

Types:

Node = node()

Flag = boolean()

Monitors the status of the node Node. If Flag
is true, monitoring is turned on; if Flag is
false, monitoring is turned off.

Making several calls to monitor_node(Node, true) for
the same Node is not an error; it results in as many,
completely independent, monitorings.

If Node fails or does not exist, the message
{nodedown, Node} is delivered to the process. If a
process has made two calls to monitor_node(Node, true)
and Node terminates, two nodedown messages are
delivered to the process. If there is no connection to
Node, there will be an attempt to create one. If this
fails, a nodedown message is delivered.

Nodes connected through hidden connections can be monitored
as any other node.

Failure: badargif the local node is not alive.

erlang:monitor_node(Node, Flag, Options) -> true

Types:

Node = node()

Flag = boolean()

Options = [Option]

Option = allow_passive_connect

Behaves as monitor_node/2 except that it allows an
extra option to be given, namely allow_passive_connect.
The option allows the BIF to wait the normal net connection
timeout for the monitored node to connect itself,
even if it cannot be actively connected from this node
(i.e. it is blocked). The state where this might be useful can
only be achieved by using the kernel option
dist_auto_connect once. If that kernel option is not
used, the allow_passive_connect option has no
effect.

Note

The allow_passive_connect option is used
internally and is seldom needed in applications where the
network topology and the kernel options in effect is known in
advance.

Failure: badarg if the local node is not alive or the
option list is malformed.

erlang:nif_error(Reason) -> no_return()

Types:

Reason = term()

Works exactly like
erlang:error/1,
but Dialyzer thinks that this BIF will return an arbitrary term.
When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
will not generate false warnings.

erlang:nif_error(Reason, Args) -> no_return()

Types:

Reason = term()

Args = [term()]

Works exactly like
erlang:error/2,
but Dialyzer thinks that this BIF will return an arbitrary term.
When used in a stub function for a NIF to generate an
exception when the NIF library is not loaded, Dialyzer
will not generate false warnings.

node() -> Node

Types:

Node = node()

Returns the name of the local node. If the node is not alive,
nonode@nohost is returned instead.

Allowed in guard tests.

node(Arg) -> Node

Types:

Arg = pid() | port() | reference()

Node = node()

Returns the node where Arg is located. Arg can
be a pid, a reference, or a port. If the local node is not
alive, nonode@nohost is returned.

Allowed in guard tests.

nodes() -> Nodes

Types:

Nodes = [node()]

Returns a list of all visible nodes in the system, excluding
the local node. Same as nodes(visible).

nodes(Arg) -> Nodes

Types:

Arg = NodeType | [NodeType]

NodeType = visible | hidden | connected | this | known

Nodes = [node()]

Returns a list of nodes according to argument given.
The result returned when the argument is a list, is the list
of nodes satisfying the disjunction(s) of the list elements.

NodeType can be any of the following:

visible

Nodes connected to this node through normal connections.

hidden

Nodes connected to this node through hidden connections.

connected

All nodes connected to this node.

this

This node.

known

Nodes which are known to this node, i.e., connected,
previously connected, etc.

Returns the tuple {MegaSecs, Secs, MicroSecs} which is
the elapsed time since 00:00 GMT, January 1, 1970 (zero hour)
on the assumption that the underlying OS supports this.
Otherwise, some other point in time is chosen. It is also
guaranteed that subsequent calls to this BIF returns
continuously increasing values. Hence, the return value from
now() can be used to generate unique time-stamps,
and if it is called in a tight loop on a fast machine
the time of the node can become skewed.

It can only be used to check the local time of day if
the time-zone info of the underlying operating system is
properly configured.

If you do not need the return value to be unique and
monotonically increasing, use
os:timestamp/0
instead to avoid some overhead.

Returns a port identifier as the result of opening a
new Erlang port. A port can be seen as an external Erlang
process. PortName is one of the following:

{spawn, Command}

Starts an external program. Command is the name
of the external program which will be run. Command
runs outside the Erlang work space unless an Erlang
driver with the name Command is found. If found,
that driver will be started. A driver runs in the Erlang
workspace, which means that it is linked with the Erlang
runtime system.

When starting external programs on Solaris, the system
call vfork is used in preference to fork
for performance reasons, although it has a history of
being less robust. If there are problems with using
vfork, setting the environment variable
ERL_NO_VFORK to any value will cause fork
to be used instead.

For external programs, the PATH is searched
(or an equivalent method is used to find programs,
depending on operating system). This is done by invoking
the shell on certain platforms. The first space
separated token of the command will be considered as the
name of the executable (or driver). This (among other
things) makes this option unsuitable for running
programs having spaces in file or directory names. Use
{spawn_executable, Command} instead if spaces in executable
file names is desired.

{spawn_driver, Command}

Works like {spawn, Command}, but demands the
first (space separated) token of the command to be the name of a
loaded driver. If no driver with that name is loaded, a
badarg error is raised.

{spawn_executable, FileName}

Works like {spawn, FileName}, but only runs
external executables. The FileName in its whole
is used as the name of the executable, including any
spaces. If arguments are to be passed, the
args and arg0PortSettings can be used.

The shell is not usually invoked to start the
program, it's executed directly. Neither is the
PATH (or equivalent) searched. To find a program
in the PATH to execute, use os:find_executable/1.

Only if a shell script or .bat file is
executed, the appropriate command interpreter will
implicitly be invoked, but there will still be no
command argument expansion or implicit PATH search.

The name of the executable as well as the arguments
given in args and arg0 is subject to
Unicode file name translation if the system is running
in Unicode file name mode. To avoid
translation or force i.e. UTF-8, supply the executable
and/or arguments as a binary in the correct
encoding. See the file module, the
file:native_name_encoding/0 function and the
stdlib users guide
for details.

Note

The characters in the name (if given as a list)
can only be > 255 if the Erlang VM is started in
Unicode file name translation mode, otherwise the name
of the executable is limited to the ISO-latin-1
character set.

If the FileName cannot be run, an error
exception, with the posix error code as the reason, is
raised. The error reason may differ between operating
systems. Typically the error enoent is raised
when one tries to run a program that is not found and
eaccess is raised when the given file is not
executable.

{fd, In, Out}

Allows an Erlang process to access any currently opened
file descriptors used by Erlang. The file descriptor
In can be used for standard input, and the file
descriptor Out for standard output. It is only
used for various servers in the Erlang operating system
(shell and user). Hence, its use is very
limited.

PortSettings is a list of settings for the port.
Valid settings are:

{packet, N}

Messages are preceded by their length, sent in N
bytes, with the most significant byte first. Valid values
for N are 1, 2, or 4.

stream

Output messages are sent without packet lengths. A
user-defined protocol must be used between the Erlang
process and the external object.

{line, L}

Messages are delivered on a per line basis. Each line
(delimited by the OS-dependent newline sequence) is
delivered in one single message. The message data format
is {Flag, Line}, where Flag is either
eol or noeol and Line is the actual
data delivered (without the newline sequence).

L specifies the maximum line length in bytes.
Lines longer than this will be delivered in more than one
message, with the Flag set to noeol for all
but the last message. If end of file is encountered
anywhere else than immediately following a newline
sequence, the last line will also be delivered with
the Flag set to noeol. In all other cases,
lines are delivered with Flag set to eol.

The {packet, N} and {line, L} settings are
mutually exclusive.

{cd, Dir}

This is only valid for {spawn, Command} and
{spawn_executable, FileName}.
The external program starts using Dir as its
working directory. Dir must be a string.

{env, Env}

This is only valid for {spawn, Command} and
{spawn_executable, FileName}.
The environment of the started process is extended using
the environment specifications in Env.

Env should be a list of tuples {Name, Val},
where Name is the name of an environment variable,
and Val is the value it is to have in the spawned
port process. Both Name and Val must be
strings. The one exception is Val being the atom
false (in analogy with os:getenv/1), which
removes the environment variable.

If Unicode filename encoding is in effect (see the erl manual
page), the strings (both Name and
Value) may contain characters with codepoints > 255.

{args, [ string() | binary() ]}

This option is only valid for {spawn_executable, FileName}
and specifies arguments to the executable. Each argument
is given as a separate string and (on Unix) eventually
ends up as one element each in the argument vector. On
other platforms, similar behavior is mimicked.

The arguments are not expanded by the shell prior to
being supplied to the executable, most notably this
means that file wildcard expansion will not happen. Use
filelib:wildcard/1
to expand wildcards for the arguments. Note that even if
the program is a Unix shell script, meaning that the
shell will ultimately be invoked, wildcard expansion
will not happen and the script will be provided with the
untouched arguments. On Windows®, wildcard expansion
is always up to the program itself, why this isn't an
issue.

Note also that the actual executable name (a.k.a. argv[0])
should not be given in this list. The proper executable name will
automatically be used as argv[0] where applicable.

When the Erlang VM is running in Unicode file name
mode, the arguments can contain any Unicode characters and
will be translated into whatever is appropriate on the
underlying OS, which means UTF-8 for all platforms except
Windows, which has other (more transparent) ways of
dealing with Unicode arguments to programs. To avoid
Unicode translation of arguments, they can be supplied as
binaries in whatever encoding is deemed appropriate.

Note

The characters in the arguments (if given as a
list of characters) can only be > 255 if the Erlang
VM is started in Unicode file name mode,
otherwise the arguments are limited to the
ISO-latin-1 character set.

If one, for any reason, wants to explicitly set the
program name in the argument vector, the arg0
option can be used.

{arg0, string() | binary()}

This option is only valid for {spawn_executable, FileName}
and explicitly specifies the program name argument when
running an executable. This might in some circumstances,
on some operating systems, be desirable. How the program
responds to this is highly system dependent and no specific
effect is guaranteed.

The unicode file name translation rules of the
args option apply to this option as well.

exit_status

This is only valid for {spawn, Command} where
Command refers to an external program, and for
{spawn_executable, FileName}.

When the external process connected to the port exits, a
message of the form {Port,{exit_status,Status}} is
sent to the connected process, where Status is the
exit status of the external process. If the program
aborts, on Unix the same convention is used as the shells
do (i.e., 128+signal).

If the eof option has been given as well,
the eof message and the exit_status message
appear in an unspecified order.

If the port program closes its stdout without exiting,
the exit_status option will not work.

use_stdio

This is only valid for {spawn, Command} and
{spawn_executable, FileName}. It
allows the standard input and output (file descriptors 0
and 1) of the spawned (UNIX) process for communication
with Erlang.

nouse_stdio

The opposite of use_stdio. Uses file descriptors
3 and 4 for communication with Erlang.

stderr_to_stdout

Affects ports to external programs. The executed program
gets its standard error file redirected to its standard
output file. stderr_to_stdout and
nouse_stdio are mutually exclusive.

overlapped_io

Affects ports to external programs on Windows® only.
The standard input and standard output handles of the port program
will, if this option is supplied, be opened with the flag
FILE_FLAG_OVERLAPPED, so that the port program can (and has to) do
overlapped I/O on its standard handles. This is not normally
the case for simple port programs, but an option of value for the
experienced Windows programmer. On all other platforms, this
option is silently discarded.

in

The port can only be used for input.

out

The port can only be used for output.

binary

All IO from the port are binary data objects as opposed
to lists of bytes.

eof

The port will not be closed at the end of the file and
produce an exit signal. Instead, it will remain open and
a {Port, eof} message will be sent to the process
holding the port.

hide

When running on Windows, suppress creation of a new
console window when spawning the port program.
(This option has no effect on other platforms.)

Set scheduler hint for port parallelism. If set to true,
the VM will schedule port tasks when it by this can improve the
parallelism in the system. If set to false, the VM will
try to perform port tasks immediately and by this improving the
latency at the expense of parallelism. The default can be set on
system startup by passing the
+spp command line argument
to erl(1).

The default is stream for all types of port and
use_stdio for spawned ports.

Failure: If the port cannot be opened, the exit reason is
badarg, system_limit, or the Posix error code which
most closely describes the error, or einval if no Posix code
is appropriate:

badarg

Bad input arguments to open_port.

system_limit

All available ports in the Erlang emulator are in use.

enomem

There was not enough memory to create the port.

eagain

There are no more available operating system processes.

enametoolong

The external command given was too long.

emfile

There are no more available file descriptors (for the operating system process
that the Erlang emulator runs in).

enfile

The file table is full (for the entire operating system).

eacces

The Command given in {spawn_executable, Command} does not point out an executable file.

enoent

The FileName given in {spawn_executable, FileName} does not point out an existing file.

During use of a port opened using {spawn, Name},
{spawn_driver, Name} or {spawn_executable, Name},
errors arising when sending messages to it are reported to
the owning process using signals of the form
{'EXIT', Port, PosixCode}. See file(3) for
possible values of PosixCode.

The maximum number of ports that can be open at the same
time can be configured by passing the
+Q
command line flag to
erl(1).

erlang:phash(Term, Range) -> Hash

Types:

Term = term()

Range = Hash = integer() >= 1

Range = 1..2^32, Hash = 1..Range

Portable hash function that will give the same hash for
the same Erlang term regardless of machine architecture and
ERTS version (the BIF was introduced in ERTS 4.9.1.1). Range
can be between 1 and 2^32, the function returns a hash value
for Term within the range 1..Range.

This BIF could be used instead of the old deprecated
erlang:hash/2 BIF, as it calculates better hashes for
all data-types, but consider using phash2/1,2 instead.

erlang:phash2(Term) -> Hasherlang:phash2(Term, Range) -> Hash

Types:

Term = term()

Range = integer() >= 1

1..2^32

Hash = integer() >= 0

0..Range-1

Portable hash function that will give the same hash for
the same Erlang term regardless of machine architecture and
ERTS version (the BIF was introduced in ERTS 5.2). Range can
be between 1 and 2^32, the function returns a hash value for
Term within the range 0..Range-1. When called
without the Range argument, a value in the range
0..2^27-1 is returned.

This BIF should always be used for hashing terms. It
distributes small integers better than phash/2, and
it is faster for bignums and binaries.

Note that the range 0..Range-1 is different from
the range of phash/2 (1..Range).

pid_to_list(Pid) -> string()

Types:

Pid = pid()

Returns a string which corresponds to the text
representation of Pid.

Warning

This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.

port_close(Port) -> true

Types:

Port = port() | atom()

Closes an open port. Roughly the same as
Port ! {self(), close} except for the error behaviour
(see below), being synchronous, and that the port does
not reply with {Port, closed}. Any process may
close a port with port_close/1, not only the port owner
(the connected process).

For comparison: Port ! {self(), close} fails with
badarg if Port cannot be sent to (i.e.,
Port refers neither to a port nor to a process). If
Port is a closed port nothing happens. If Port
is an open port and the calling process is the port owner,
the port replies with {Port, closed} when all buffers
have been flushed and the port really closes, but if
the calling process is not the port owner the port owner fails with badsig.

Note that any process can close a port using
Port ! {PortOwner, close} just as if it itself was
the port owner, but the reply always goes to the port owner.

As of OTP-R16 Port ! {PortOwner, close} is truly
asynchronous. Note that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_close/1 is
however still fully synchronous. This due to its error
behavior.

Failure: badarg if Port is not an open port or
the registered name of an open port.

port_command(Port, Data) -> true

Types:

Port = port() | atom()

Data = iodata()

Sends data to a port. Same as
Port ! {PortOwner, {command, Data}} except for the error
behaviour and being synchronous (see below). Any process may
send data to a port with port_command/2, not only the
port owner (the connected process).

For comparison: Port ! {PortOwner, {command, Data}}
fails with badarg if Port cannot be sent to
(i.e., Port refers neither to a port nor to a process).
If Port is a closed port the data message disappears
without a sound. If Port is open and the calling
process is not the port owner, the port owner fails
with badsig. The port owner fails with badsig
also if Data is not a valid IO list.

Note that any process can send to a port using
Port ! {PortOwner, {command, Data}} just as if it
itself was the port owner.

If the port is busy, the calling process will be suspended
until the port is not busy anymore.

As of OTP-R16 Port ! {PortOwner, {command, Data}} is
truly asynchronous. Note that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_command/2 is
however still fully synchronous. This due to its error
behavior.

If the port command is aborted false is returned;
otherwise, true is returned.

If the port is busy, the calling process will be suspended
until the port is not busy anymore.

Currently the following Options are valid:

force

The calling process will not be suspended if the port is
busy; instead, the port command is forced through. The
call will fail with a notsup exception if the
driver of the port does not support this. For more
information see the
ERL_DRV_FLAG_SOFT_BUSY
driver flag.

nosuspend

The calling process will not be suspended if the port is
busy; instead, the port command is aborted and
false is returned.

Note

More options may be added in the future.

Failures:

badarg

If Port is not an open port or the registered name
of an open port.

badarg

If Data is not a valid io list.

badarg

If OptionList is not a valid option list.

notsup

If the force option has been passed, but the
driver of the port does not allow forcing through
a busy port.

port_connect(Port, Pid) -> true

Types:

Port = port() | atom()

Pid = pid()

Sets the port owner (the connected port) to Pid.
Roughly the same as Port ! {Owner, {connect, Pid}}
except for the following:

The error behavior differs, see below.

The port does not reply with
{Port,connected}.

port_connect/1 is synchronous, see below.

The new port owner gets linked to the port.

The old port owner stays linked to the port and have to call
unlink(Port) if this is not desired. Any process may
set the port owner to be any process with
port_connect/2.

For comparison: Port ! {self(), {connect, Pid}} fails
with badarg if Port cannot be sent to (i.e.,
Port refers neither to a port nor to a process). If
Port is a closed port nothing happens. If Port
is an open port and the calling process is the port owner,
the port replies with {Port, connected} to the old
port owner. Note that the old port owner is still linked to
the port, and that the new is not. If Port is an open
port and the calling process is not the port owner,
the port owner fails with badsig. The port
owner fails with badsig also if Pid is not an
existing local pid.

Note that any process can set the port owner using
Port ! {PortOwner, {connect, Pid}} just as if it
itself was the port owner, but the reply always goes to
the port owner.

As of OTP-R16 Port ! {PortOwner, {connect, Pid}} is
truly asynchronous. Note that this operation has always been
documented as an asynchronous operation, while the underlying
implementation has been synchronous. port_connect/2 is
however still fully synchronous. This due to its error
behavior.

Failure: badarg if Port is not an open port
or the registered name of an open port, or if Pid is
not an existing local pid.

port_control(Port, Operation, Data) -> iodata() | binary()

Types:

Port = port() | atom()

Operation = integer()

Data = iodata()

Performs a synchronous control operation on a port.
The meaning of Operation and Data depends on
the port, i.e., on the port driver. Not all port drivers
support this control feature.

Returns: a list of integers in the range 0 through 255, or a
binary, depending on the port driver. The meaning of
the returned data also depends on the port driver.

Failure: badarg if Port is not an open port or
the registered name of an open port, if Operation
cannot fit in a 32-bit integer, if the port driver does not
support synchronous control operations, or if the port driver
so decides for any reason (probably something wrong with
Operation or Data).

erlang:port_call(Port, Operation, Data) -> term()

Types:

Port = port() | atom()

Operation = integer()

Data = term()

Performs a synchronous call to a port. The meaning of
Operation and Data depends on the port, i.e.,
on the port driver. Not all port drivers support this feature.

Port is a port identifier, referring to a driver.

Operation is an integer, which is passed on to
the driver.

Data is any Erlang term. This data is converted to
binary term format and sent to the port.

Returns: a term from the driver. The meaning of the returned
data also depends on the port driver.

Failure: badarg if Port is not an open port or
the registered name of an open port, if Operation
cannot fit in a 32-bit integer, if the port driver does not
support synchronous control operations, or if the port driver
so decides for any reason (probably something wrong with
Operation or Data).

Returns a list containing tuples with information about
the Port, or undefined if the port is not open.
The order of the tuples is not defined, nor are all the
tuples mandatory.

Currently the result will containt information about the
following Items: registered_name (if the port has
a registered name), id, connected, links,
name, input, and output. For more information
about the different Items, see
port_info/2.

Locking is currently either false
(emulator without SMP support), port_level (port specific
locking), or driver_level (driver specific locking). Note
that these results are highly implementation specific and might
change in the future.

If the port identified by Port is not open,
undefined is returned.

Failure: badarg if Port is not a local
port identifier, or an atom.

erlang:port_info(Port, Item :: memory) -> {memory, Bytes} | undefined

Types:

Port = port() | atom()

Bytes = integer() >= 0

Bytes is the total amount of memory,
in bytes, allocated for this port by the runtime system. Note
that the port itself might have allocated memory which is not
included in Bytes.

RegisteredName is the registered name of
the port. If the port has no registered name, [] is returned.

If the port identified by Port is not open,
undefined is returned.

Failure: badarg if Port is not a local
port identifier, or an atom.

erlang:port_to_list(Port) -> string()

Types:

Port = port()

Returns a string which corresponds to the text
representation of the port identifier Port.

Warning

This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.

erlang:ports() -> [port()]

Returns a list of port identifiers corresponding to all the
ports currently existing on the local node.

Note that a port that is exiting, exists but is not open.

pre_loaded() -> [module()]

Returns a list of Erlang modules which are pre-loaded in
the system. As all loading of code is done through the file
system, the file system must have been loaded previously.
Hence, at least the module init must be pre-loaded.

erlang:process_display(Pid, Type) -> true

Types:

Pid = pid()

Type = backtrace

Writes information about the local process Pid on
standard error. The currently allowed value for the atom
Type is backtrace, which shows the contents of
the call stack, including information about the call chain, with
the current function printed first. The format of the output
is not further defined.

process_flag(Flag :: trap_exit, Boolean) -> OldBoolean

Types:

Boolean = OldBoolean = boolean()

When trap_exit is set to true, exit signals
arriving to a process are converted to {'EXIT', From, Reason} messages, which can be received as ordinary
messages. If trap_exit is set to false, the
process exits if it receives an exit signal other than
normal and the exit signal is propagated to its
linked processes. Application processes should normally
not trap exits.

This is used by a process to redefine the error handler
for undefined function calls and undefined registered
processes. Inexperienced users should not use this flag
since code auto-loading is dependent on the correct
operation of the error handling module.

This changes the minimum binary virtual heap size for the calling
process.

Returns the old value of the flag.

process_flag(Flag :: priority, Level) -> OldLevel

Types:

Level = OldLevel = priority_level()

priority_level() = low | normal | high | max

This sets the process priority. Level is an atom.
There are currently four priority levels: low,
normal, high, and max. The default
priority level is normal. NOTE: The
max priority level is reserved for internal use in
the Erlang runtime system, and should not be used
by others.

Internally in each priority level processes are scheduled
in a round robin fashion.

Execution of processes on priority normal and
priority low will be interleaved. Processes on
priority low will be selected for execution less
frequently than processes on priority normal.

When there are runnable processes on priority high
no processes on priority low, or normal will
be selected for execution. Note, however, that this does
not mean that no processes on priority low,
or normal will be able to run when there are
processes on priority high running. On the runtime
system with SMP support there might be more processes running
in parallel than processes on priority high, i.e.,
a low, and a high priority process might
execute at the same time.

When there are runnable processes on priority max
no processes on priority low, normal, or
high will be selected for execution. As with the
high priority, processes on lower priorities might
execute in parallel with processes on priority max.

Scheduling is preemptive. Regardless of priority, a process
is preempted when it has consumed more than a certain amount
of reductions since the last time it was selected for
execution.

NOTE: You should not depend on the scheduling
to remain exactly as it is today. Scheduling, at least on
the runtime system with SMP support, is very likely to be
modified in the future in order to better utilize available
processor cores.

There is currently no automatic mechanism for
avoiding priority inversion, such as priority inheritance,
or priority ceilings. When using priorities you have
to take this into account and handle such scenarios by
yourself.

Making calls from a high priority process into code
that you don't have control over may cause the high
priority process to wait for a processes with lower
priority, i.e., effectively decreasing the priority of the
high priority process during the call. Even if this
isn't the case with one version of the code that you don't
have under your control, it might be the case in a future
version of it. This might, for example, happen if a
high priority process triggers code loading, since
the code server runs on priority normal.

Other priorities than normal are normally not needed.
When other priorities are used, they need to be used
with care, especially the high priority must
be used with care. A process on high priority should
only perform work for short periods of time. Busy looping for
long periods of time in a high priority process will
most likely cause problems, since there are important servers
in OTP running on priority normal.

Returns the old value of the flag.

process_flag(Flag :: save_calls, N) -> OldN

Types:

N = OldN = 0..10000

N must be an integer in the interval 0..10000.
If N > 0, call saving is made active for the
process, which means that information about the N
most recent global function calls, BIF calls, sends and
receives made by the process are saved in a list, which
can be retrieved with
process_info(Pid, last_calls). A global function
call is one in which the module of the function is
explicitly mentioned. Only a fixed amount of information
is saved: a tuple {Module, Function, Arity} for
function calls, and the mere atoms send,
'receive' and timeout for sends and receives
('receive' when a message is received and
timeout when a receive times out). If N = 0,
call saving is disabled for the process, which is the
default. Whenever the size of the call saving list is set,
its contents are reset.

Returns the old value of the flag.

process_flag(Flag :: sensitive, Boolean) -> OldBoolean

Types:

Boolean = OldBoolean = boolean()

Set or clear the sensitive flag for the current process.
When a process has been marked as sensitive by calling
process_flag(sensitive, true), features in the run-time
system that can be used for examining the data and/or inner working
of the process are silently disabled.

Features that are disabled include (but are not limited to)
the following:

Tracing: Trace flags can still be set for the process, but no
trace messages of any kind will be generated.
(If the sensitive flag is turned off, trace messages will
again be generated if there are any trace flags set.)

Sequential tracing: The sequential trace token will be propagated
as usual, but no sequential trace messages will be generated.

process_info/1,2 cannot be used to read out the message
queue or the process dictionary (both will be returned as empty lists).

Stack back-traces cannot be displayed for the process.

In crash dumps, the stack, messages, and the process dictionary
will be omitted.

If {save_calls,N} has been set for the process, no
function calls will be saved to the call saving list.
(The call saving list will not be cleared; furthermore, send, receive,
and timeout events will still be added to the list.)

Returns the old value of the flag.

process_flag(Pid, Flag, Value) -> OldValue

Types:

Pid = pid()

Flag = save_calls

Value = OldValue = integer() >= 0

Sets certain flags for the process Pid, in the same
manner as
process_flag/2.
Returns the old value of the flag. The allowed values for
Flag are only a subset of those allowed in
process_flag/2, namely: save_calls.

Returns a list containing InfoTuples with
miscellaneous information about the process identified by
Pid, or undefined if the process is not alive.

The order of the InfoTuples is not defined, nor
are all the InfoTuples mandatory. The InfoTuples
part of the result may be changed without prior notice.
Currently InfoTuples with the following items
are part of the result:
current_function, initial_call, status,
message_queue_len, messages, links,
dictionary, trap_exit, error_handler,
priority, group_leader, total_heap_size,
heap_size, stack_size, reductions, and
garbage_collection.
If the process identified by Pid has a registered name
also an InfoTuple with the item registered_name
will appear.

Returns information about the process identified by Pid
as specified by the Item or the ItemList, or undefined if the
process is not alive.

If the process is alive and a single Item is given,
the returned value is the corresponding
InfoTuple unless Item =:= registered_name
and the process has no registered name. In this case
[] is returned. This strange behavior is due to
historical reasons, and is kept for backward compatibility.

If an ItemList is given, the result is an
InfoTupleList. The InfoTuples in the
InfoTupleList will appear with the corresponding
Items in the same order as the Items appeared
in the ItemList. Valid Items may appear multiple
times in the ItemList.

Note

If registered_name is part of an ItemList
and the process has no name registered a
{registered_name, []}InfoTuplewill
appear in the resulting InfoTupleList. This
behavior is different than when a single
Item =:= registered_name is given, and than when
process_info/1 is used.

Currently the following InfoTuples with corresponding
Items are valid:

{backtrace, Bin}

The binary Bin contains the same information as
the output from
erlang:process_display(Pid, backtrace). Use
binary_to_list/1 to obtain the string of characters
from the binary.

{binary, BinInfo}

BinInfo is a list containing miscellaneous information
about binaries currently being referred to by this process.
This InfoTuple may be changed or removed without prior
notice.

{catchlevel, CatchLevel}

CatchLevel is the number of currently active
catches in this process. This InfoTuple may be
changed or removed without prior notice.

{current_function, {Module, Function, Arity}}

Module, Function, Arity is
the current function call of the process.

{current_location, {Module, Function, Arity, Location}}

Module, Function, Arity is
the current function call of the process.
Location is a list of two-tuples that describes the
location in the source code.

{current_stacktrace, Stack}

Return the current call stack back-trace (stacktrace)
of the process. The stack has the same format as returned by
erlang:get_stacktrace/0.

{dictionary, Dictionary}

Dictionary is the dictionary of the process.

{error_handler, Module}

Module is the error handler module used by
the process (for undefined function calls, for example).

{garbage_collection, GCInfo}

GCInfo is a list which contains miscellaneous
information about garbage collection for this process.
The content of GCInfo may be changed without
prior notice.

{group_leader, GroupLeader}

GroupLeader is group leader for the IO of
the process.

{heap_size, Size}

Size is the size in words of youngest heap generation
of the process. This generation currently include the stack
of the process. This information is highly implementation
dependent, and may change if the implementation change.

{initial_call, {Module, Function, Arity}}

Module, Function, Arity is
the initial function call with which the process was
spawned.

{links, PidsAndPorts}

PidsAndPorts is a list of pids and
port identifiers, with processes or ports to which the process
has a link.

{last_calls, false|Calls}

The value is false if call saving is not active
for the process (see
process_flag/3).
If call saving is active, a list is returned, in which
the last element is the most recent called.

{memory, Size}

Size is the size in bytes of the process. This
includes call stack, heap and internal structures.

{message_queue_len, MessageQueueLen}

MessageQueueLen is the number of messages
currently in the message queue of the process. This is
the length of the list MessageQueue returned as
the info item messages (see below).

{messages, MessageQueue}

MessageQueue is a list of the messages to
the process, which have not yet been processed.

{min_heap_size, MinHeapSize}

MinHeapSize is the minimum heap size for the process.

{min_bin_vheap_size, MinBinVHeapSize}

MinBinVHeapSize is the minimum binary virtual heap size for the process.

{monitored_by, Pids}

A list of pids that are monitoring the process (with
monitor/2).

{monitors, Monitors}

A list of monitors (started by monitor/2)
that are active for the process. For a local process
monitor or a remote process monitor by pid, the list item
is {process, Pid}, and for a remote process
monitor by name, the list item is
{process, {RegName, Node}}.

Atom is the registered name of the process. If
the process has no registered name, this tuple is not
present in the list.

{sequential_trace_token, [] | SequentialTraceToken}

SequentialTraceToken the sequential trace token for
the process. This InfoTuple may be changed or removed
without prior notice.

{stack_size, Size}

Size is the stack size of the process in words.

{status, Status}

Status is the status of the process. Status
is exiting, garbage_collecting,
waiting (for a message), running,
runnable (ready to run, but another process is
running), or suspended (suspended on a "busy" port
or by the erlang:suspend_process/[1,2] BIF).

{suspending, SuspendeeList}

SuspendeeList is a list of {Suspendee,
ActiveSuspendCount, OutstandingSuspendCount} tuples.
Suspendee is the pid of a process that have been or is to
be suspended by the process identified by Pid via the
erlang:suspend_process/2
BIF, or the
erlang:suspend_process/1
BIF. ActiveSuspendCount is the number of times the
Suspendee has been suspended by Pid.
OutstandingSuspendCount is the number of not yet
completed suspend requests sent by Pid. That is,
if ActiveSuspendCount =/= 0, Suspendee is
currently in the suspended state, and if
OutstandingSuspendCount =/= 0 the asynchronous
option of erlang:suspend_process/2 has been used and
the suspendee has not yet been suspended by Pid.
Note that the ActiveSuspendCount and
OutstandingSuspendCount are not the total suspend count
on Suspendee, only the parts contributed by Pid.

{total_heap_size, Size}

Size is the total size in words of all heap
fragments of the process. This currently include the stack
of the process.

{trace, InternalTraceFlags}

InternalTraceFlags is an integer representing
internal trace flag for this process. This InfoTuple
may be changed or removed without prior notice.

{trap_exit, Boolean}

Boolean is true if the process is trapping
exits, otherwise it is false.

Note however, that not all implementations support every one
of the above Items.

Failure: badarg if Pid is not a local process,
or if Item is not a valid Item.

processes() -> [pid()]

Returns a list of process identifiers corresponding to
all the processes currently existing on the local node.

Note that a process that is exiting, exists but is not alive, i.e.,
is_process_alive/1 will return false for a process
that is exiting, but its process identifier will be part
of the result returned from processes/0.

> processes().
[<0.0.0>,<0.2.0>,<0.4.0>,<0.5.0>,<0.7.0>,<0.8.0>]

purge_module(Module) -> true

Types:

Module = atom()

Removes old code for Module. Before this BIF is used,
erlang:check_process_code/2 should be called to check
that no processes are executing old code in the module.

Warning

This BIF is intended for the code server (see
code(3)) and should not be
used elsewhere.

Failure: badarg if there is no old code for
Module.

put(Key, Val) -> term()

Types:

Key = Val = term()

Adds a new Key to the process dictionary, associated
with the value Val, and returns undefined. If
Key already exists, the old value is deleted and
replaced by Val and the function returns the old value.

Note

The values stored when put is evaluated within
the scope of a catch will not be retracted if a
throw is evaluated, or if an error occurs.

Stops the execution of the calling process with an
exception of given class, reason and call stack backtrace
(stacktrace).

Warning

This BIF is intended for debugging and for use in
the Erlang operating system. In general, it should
be avoided in applications, unless you know
very well what you are doing.

Class is one of error, exit or
throw, so if it were not for the stacktrace
erlang:raise(Class, Reason, Stacktrace) is
equivalent to erlang:Class(Reason).
Reason is any term and Stacktrace is a list as
returned from get_stacktrace(), that is a list of
4-tuples {Module, Function, Arity | Args,
Location} where Module and Function
are atoms and the third element is an integer arity or an
argument list. The stacktrace may also contain {Fun,
Args, Location} tuples where
Fun is a local fun and Args is an argument list.

The Location element at the end is optional.
Omitting it is equivalent to specifying an empty list.

The stacktrace is used as the exception stacktrace for the
calling process; it will be truncated to the current
maximum stacktrace depth.

Because evaluating this function causes the process to
terminate, it has no return value - unless the arguments are
invalid, in which case the function returns the error reason, that is badarg. If you want to be
really sure not to return you can call
error(erlang:raise(Class, Reason, Stacktrace))
and hope to distinguish exceptions later.

erlang:read_timer(TimerRef) -> integer() >= 0 | false

Types:

TimerRef = reference()

TimerRef is a timer reference returned by
erlang:send_after/3
or
erlang:start_timer/3.
If the timer is active, the function returns the time in
milliseconds left until the timer will expire, otherwise
false (which means that TimerRef was never a
timer, that it has been cancelled, or that it has already
delivered its message).

This BIF is intended for debugging and for use in
the Erlang operating system. It should not be used in
application programs.

register(RegName, PidOrPort) -> true

Types:

RegName = atom()

PidOrPort = port() | pid()

Associates the name RegName with a pid or a port
identifier. RegName, which must be an atom, can be used
instead of the pid / port identifier in the send operator
(RegName ! Message).

> register(db, Pid).
true

Failure: badarg if PidOrPort is not an existing,
local process or port, if RegName is already in use,
if the process or port is already registered (already has a
name), or if RegName is the atom undefined.

Decreases the suspend count on the process identified by
Suspendee. Suspendee should previously have been
suspended via
erlang:suspend_process/2,
or
erlang:suspend_process/1
by the process calling erlang:resume_process(Suspendee). When
the suspend count on Suspendee reach zero, Suspendee
will be resumed, i.e., the state of the Suspendee is changed
from suspended into the state Suspendee was in before it was
suspended.

Warning

This BIF is intended for debugging only.

Failures:

badarg

If Suspendee isn't a process identifier.

badarg

If the process calling erlang:resume_process/1 had
not previously increased the suspend count on the process
identified by Suspendee.

Sends a message and returns ok, or does not send
the message but returns something else (see below). Otherwise
the same as
erlang:send/2. See
also
erlang:send_nosuspend/2,3.
for more detailed explanation and warnings.

The possible options are:

nosuspend

If the sender would have to be suspended to do the send,
nosuspend is returned instead.

noconnect

If the destination node would have to be auto-connected
before doing the send, noconnect is returned
instead.

Warning

As with erlang:send_nosuspend/2,3: Use with extreme
care!

erlang:send_after(Time, Dest, Msg) -> TimerRef

Types:

Time = integer() >= 0

0 <= Time <= 4294967295

Dest = pid() | atom()

Msg = term()

TimerRef = reference()

Starts a timer which will send the message Msg
to Dest after Time milliseconds.

If Dest is a pid() it has to be a pid() of a local process, dead or alive.

The Time value can, in the current implementation, not be greater than 4294967295.

If Dest is an atom(), it is supposed to be the name of
a registered process. The process referred to by the name is
looked up at the time of delivery. No error is given if
the name does not refer to a process.

If Dest is a pid(), the timer will be automatically
canceled if the process referred to by the pid() is not alive,
or when the process exits. This feature was introduced in
erts version 5.4.11. Note that timers will not be
automatically canceled when Dest is an atom.

The same as
erlang:send(Dest, Msg, [nosuspend]), but returns true if
the message was sent and false if the message was not
sent because the sender would have had to be suspended.

This function is intended for send operations towards an
unreliable remote node without ever blocking the sending
(Erlang) process. If the connection to the remote node
(usually not a real Erlang node, but a node written in C or
Java) is overloaded, this function will not send the message but return false instead.

The same happens, if Dest refers to a local port that
is busy. For all other destinations (allowed for the ordinary
send operator '!') this function sends the message and
returns true.

This function is only to be used in very rare circumstances
where a process communicates with Erlang nodes that can
disappear without any trace causing the TCP buffers and
the drivers queue to be over-full before the node will actually
be shut down (due to tick timeouts) by net_kernel. The
normal reaction to take when this happens is some kind of
premature shutdown of the other node.

Note that ignoring the return value from this function would
result in unreliable message passing, which is
contradictory to the Erlang programming model. The message is
not sent if this function returns false.

Note also that in many systems, transient states of
overloaded queues are normal. The fact that this function
returns false does not in any way mean that the other
node is guaranteed to be non-responsive, it could be a
temporary overload. Also a return value of true does
only mean that the message could be sent on the (TCP) channel
without blocking, the message is not guaranteed to have
arrived at the remote node. Also in the case of a disconnected
non-responsive node, the return value is true (mimics
the behaviour of the ! operator). The expected
behaviour as well as the actions to take when the function
returns false are application and hardware specific.

This function behaves like
erlang:send_nosuspend/2),
but takes a third parameter, a list of options. The only
currently implemented option is noconnect. The option
noconnect makes the function return false if
the remote node is not currently reachable by the local
node. The normal behaviour is to try to connect to the node,
which may stall the process for a shorter period. The use of
the noconnect option makes it possible to be
absolutely sure not to get even the slightest delay when
sending to a remote process. This is especially useful when
communicating with nodes who expect to always be
the connecting part (i.e. nodes written in C or Java).

Whenever the function returns false (either when a
suspend would occur or when noconnect was specified and
the node was not already connected), the message is guaranteed
not to have been sent.

Warning

Use with extreme care!

erlang:set_cookie(Node, Cookie) -> true

Types:

Node = node()

Cookie = atom()

Sets the magic cookie of Node to the atom
Cookie. If Node is the local node, the function
also sets the cookie of all other unknown nodes to
Cookie (see
Distributed Erlang in the Erlang Reference Manual).

Failure: function_clause if the local node is not
alive.

setelement(Index, Tuple1, Value) -> Tuple2

Types:

Index = integer() >= 1

1..tuple_size(Tuple1)

Tuple1 = Tuple2 = tuple()

Value = term()

Returns a tuple which is a copy of the argument Tuple1
with the element given by the integer argument Index
(the first element is the element with index 1) replaced by
the argument Value.

> setelement(2, {10, green, bottles}, red).
{10,red,bottles}

size(Item) -> integer() >= 0

Types:

Item = tuple() | binary()

Returns an integer which is the size of the argument
Item, which must be either a tuple or a binary.

> size({morni, mulle, bwange}).
3

Allowed in guard tests.

spawn(Fun) -> pid()

Types:

Fun = function()

Returns the pid of a new process started by the application
of Fun to the empty list []. Otherwise works
like spawn/3.

spawn(Node, Fun) -> pid()

Types:

Node = node()

Fun = function()

Returns the pid of a new process started by the application
of Fun to the empty list [] on Node. If
Node does not exist, a useless pid is returned.
Otherwise works like
spawn/3.

spawn(Module, Function, Args) -> pid()

Types:

Module = module()

Function = atom()

Args = [term()]

Returns the pid of a new process started by the application
of Module:Function to Args. The new process
created will be placed in the system scheduler queue and be
run some time later.

error_handler:undefined_function(Module, Function, Args) is evaluated by the new process if
Module:Function/Arity does not exist (where
Arity is the length of Args). The error handler
can be redefined (see
process_flag/2).
If error_handler is undefined, or the user has
redefined the default error_handler its replacement is
undefined, a failure with the reason undef will occur.

> spawn(speed, regulator, [high_speed, thin_cut]).
<0.13.1>

spawn(Node, Module, Function, Args) -> pid()

Types:

Node = node()

Module = module()

Function = atom()

Args = [term()]

Returns the pid of a new process started by the application
of Module:Function to Args on Node. If
Node does not exists, a useless pid is returned.
Otherwise works like
spawn/3.

spawn_link(Fun) -> pid()

Types:

Fun = function()

Returns the pid of a new process started by the application
of Fun to the empty list []. A link is created between
the calling process and the new process, atomically.
Otherwise works like
spawn/3.

spawn_link(Node, Fun) -> pid()

Types:

Node = node()

Fun = function()

Returns the pid of a new process started by the application
of Fun to the empty list [] on Node. A link is
created between the calling process and the new process,
atomically. If Node does not exist, a useless pid is
returned (and due to the link, an exit signal with exit
reason noconnection will be received). Otherwise works
like spawn/3.

spawn_link(Module, Function, Args) -> pid()

Types:

Module = module()

Function = atom()

Args = [term()]

Returns the pid of a new process started by the application
of Module:Function to Args. A link is created
between the calling process and the new process, atomically.
Otherwise works like
spawn/3.

spawn_link(Node, Module, Function, Args) -> pid()

Types:

Node = node()

Module = module()

Function = atom()

Args = [term()]

Returns the pid of a new process started by the application
of Module:Function to Args on Node. A
link is created between the calling process and the new
process, atomically. If Node does not exist, a useless
pid is returned (and due to the link, an exit signal with exit
reason noconnection will be received). Otherwise works
like spawn/3.

spawn_monitor(Fun) -> {pid(), reference()}

Types:

Fun = function()

Returns the pid of a new process started by the application
of Fun to the empty list [] and reference for a monitor
created to the new process.
Otherwise works like
spawn/3.

spawn_monitor(Module, Function, Args) -> {pid(), reference()}

Types:

Module = module()

Function = atom()

Args = [term()]

A new process is started by the application
of Module:Function to Args, and the process is
monitored at the same time. Returns the pid and a reference
for the monitor.
Otherwise works like
spawn/3.

Sets the priority of the new process. Equivalent to
executing
process_flag(priority, Level) in the start function of the new process,
except that the priority will be set before the process is
selected for execution for the first time. For more information
on priorities see
process_flag(priority, Level).

{fullsweep_after, Number}

This option is only useful for performance tuning.
In general, you should not use this option unless you
know that there is problem with execution times and/or
memory consumption, and you should measure to make sure
that the option improved matters.

The Erlang runtime system uses a generational garbage
collection scheme, using an "old heap" for data that has
survived at least one garbage collection. When there is
no more room on the old heap, a fullsweep garbage
collection will be done.

The fullsweep_after option makes it possible to
specify the maximum number of generational collections
before forcing a fullsweep even if there is still room on
the old heap. Setting the number to zero effectively
disables the general collection algorithm, meaning that
all live data is copied at every garbage collection.

Here are a few cases when it could be useful to change
fullsweep_after. Firstly, if binaries that are no
longer used should be thrown away as soon as possible.
(Set Number to zero.) Secondly, a process that
mostly have short-lived data will be fullsweeped seldom
or never, meaning that the old heap will contain mostly
garbage. To ensure a fullsweep once in a while, set
Number to a suitable value such as 10 or 20.
Thirdly, in embedded systems with limited amount of RAM
and no virtual memory, one might want to preserve memory
by setting Number to zero. (The value may be set
globally, see
erlang:system_flag/2.)

{min_heap_size, Size}

This option is only useful for performance tuning.
In general, you should not use this option unless you
know that there is problem with execution times and/or
memory consumption, and you should measure to make sure
that the option improved matters.

Gives a minimum heap size in words. Setting this value
higher than the system default might speed up some
processes because less garbage collection is done.
Setting too high value, however, might waste memory and
slow down the system due to worse data locality.
Therefore, it is recommended to use this option only for
fine-tuning an application and to measure the execution
time with various Size values.

{min_bin_vheap_size, VSize}

This option is only useful for performance tuning.
In general, you should not use this option unless you
know that there is problem with execution times and/or
memory consumption, and you should measure to make sure
that the option improved matters.

Gives a minimum binary virtual heap size in words. Setting this value
higher than the system default might speed up some
processes because less garbage collection is done.
Setting too high value, however, might waste memory.
Therefore, it is recommended to use this option only for
fine-tuning an application and to measure the execution
time with various VSize values.

Returns the pid of a new process started by the application
of Module:Function to Args on Node. If
Node does not exist, a useless pid is returned.
Otherwise works like
spawn_opt/4.

split_binary(Bin, Pos) -> {binary(), binary()}

Types:

Bin = binary()

Pos = integer() >= 0

0..byte_size(Bin)

Returns a tuple containing the binaries which are the result
of splitting Bin into two parts at position Pos.
This is not a destructive operation. After the operation,
there will be three binaries altogether.

Starts a timer which will send the message
{timeout, TimerRef, Msg} to Dest
after Time milliseconds.

If Dest is a pid() it has to be a pid() of a local process, dead or alive.

The Time value can, in the current implementation, not be greater than 4294967295.

If Dest is an atom(), it is supposed to be the name of
a registered process. The process referred to by the name is
looked up at the time of delivery. No error is given if
the name does not refer to a process.

If Dest is a pid(), the timer will be automatically
canceled if the process referred to by the pid() is not alive,
or when the process exits. This feature was introduced in
erts version 5.4.11. Note that timers will not be
automatically canceled when Dest is an atom().

Since erts-5.5 (OTP release R11B)
this value does not include reductions performed in current
time slices of currently scheduled processes. If an
exact value is wanted, use
statistics(exact_reductions).

> statistics(reductions).
{2046,11}

statistics(Item :: run_queue) -> integer() >= 0

Returns the length of the run queue, that is, the number
of processes that are ready to run.

statistics(Item :: runtime) -> {Total_Run_Time, Time_Since_Last_Call}

Types:

Total_Run_Time = Time_Since_Last_Call = integer() >= 0

Note that the run-time is the sum of the run-time for all
threads in the Erlang run-time system and may therefore be greater
than the wall-clock time.

Returns a list of tuples with {SchedulerId,
ActiveTime, TotalTime}, where
SchedulerId is an integer id of the scheduler, ActiveTime is
the duration the scheduler has been busy, TotalTime is the total time duration since
scheduler_wall_time
activation. The time unit is not defined and may be subject to change
between releases, operating systems and system restarts.
scheduler_wall_time should only be used to calculate relative
values for scheduler-utilization. ActiveTime can never exceed TotalTime.

The definition of a busy scheduler is when it is not idle or not
scheduling (selecting) a process or port, meaning; executing process
code, executing linked-in-driver or NIF code, executing
built-in-functions or any other runtime handling, garbage collecting
or handling any other memory management. Note, a scheduler may also be
busy even if the operating system has scheduled out the scheduler
thread.

wall_clock can be used in the same manner as
runtime, except that real time is measured as
opposed to runtime or CPU time.

erlang:suspend_process(Suspendee, OptList) -> boolean()

Types:

Suspendee = pid()

OptList = [Opt]

Opt = unless_suspending | asynchronous

Increases the suspend count on the process identified by
Suspendee and puts it in the suspended state if it isn't
already in the suspended state. A suspended process will not be
scheduled for execution until the process has been resumed.

A process can be suspended by multiple processes and can
be suspended multiple times by a single process. A suspended
process will not leave the suspended state until its suspend
count reach zero. The suspend count of Suspendee
is decreased when
erlang:resume_process(Suspendee)
is called by the same process that called
erlang:suspend_process(Suspendee). All increased suspend
counts on other processes acquired by a process will automatically be
decreased when the process terminates.

Currently the following options (Opts) are available:

asynchronous

A suspend request is sent to the process identified by
Suspendee. Suspendee will eventually suspend
unless it is resumed before it was able to suspend. The caller
of erlang:suspend_process/2 will return immediately,
regardless of whether the Suspendee has suspended yet
or not. Note that the point in time when the Suspendee
will actually suspend cannot be deduced from other events
in the system. The only guarantee given is that the
Suspendee will eventually suspend (unless it
is resumed). If the asynchronous option has not
been passed, the caller of erlang:suspend_process/2 will
be blocked until the Suspendee has actually suspended.

unless_suspending

The process identified by Suspendee will be suspended
unless the calling process already is suspending the
Suspendee. If unless_suspending is combined
with the asynchronous option, a suspend request will be
sent unless the calling process already is suspending the
Suspendee or if a suspend request already has been sent
and is in transit. If the calling process already is suspending
the Suspendee, or if combined with the asynchronous
option and a send request already is in transit,
false is returned and the suspend count on Suspendee
will remain unchanged.

If the suspend count on the process identified by
Suspendee was increased, true is returned; otherwise,
false is returned.

Warning

This BIF is intended for debugging only.

Failures:

badarg

If Suspendee isn't a process identifier.

badarg

If the process identified by Suspendee is same the process as
the process calling erlang:suspend_process/2.

badarg

If the process identified by Suspendee is not alive.

badarg

If the process identified by Suspendee resides on another node.

badarg

If OptList isn't a proper list of valid Opts.

system_limit

If the process identified by Suspendee has been suspended more
times by the calling process than can be represented by the
currently used internal data structures. The current system limit
is larger than 2 000 000 000 suspends, and it will never be less
than that.

This argument is deprecated and
scheduled for removal in erts-5.10/OTP-R16. Instead of using
this argument you are advised to use the erl command
line argument +sct.
When this argument has been removed a final CPU topology to use
will be determined at emulator boot time.

Sets the user defined CpuTopology. The user defined
CPU topology will override any automatically detected
CPU topology. By passing undefined as CpuTopology
the system will revert back to the CPU topology automatically
detected. The returned value equals the value returned
from erlang:system_info(cpu_topology) before the
change was made.

Returns the old value of the flag.

The CPU topology is used when binding schedulers to logical
processors. If schedulers are already bound when the CPU
topology is changed, the schedulers will be sent a request
to rebind according to the new CPU topology.

The user defined CPU topology can also be set by passing
the +sct command
line argument to erl.

Number is a non-negative integer which indicates
how many times generational garbage collections can be
done without forcing a fullsweep collection. The value
applies to new processes; processes already running are
not affected.

Returns the old value of the flag.

In low-memory systems (especially without virtual
memory), setting the value to 0 can help to conserve
memory.

An alternative way to set this value is through the
(operating system) environment variable
ERL_FULLSWEEP_AFTER.

Sets the default minimum heap size for processes. The
size is given in words. The new min_heap_size only
effects processes spawned after the change of
min_heap_size has been made.
The min_heap_size can be set for individual
processes by use of
spawn_opt/N or
process_flag/2.

Sets the default minimum binary virtual heap size for processes. The
size is given in words. The new min_bin_vhheap_size only
effects processes spawned after the change of
min_bin_vhheap_size has been made.
The min_bin_vheap_size can be set for individual
processes by use of
spawn_opt/N or
process_flag/2.

If multi-scheduling is enabled, more than one scheduler
thread is used by the emulator. Multi-scheduling can be
blocked. When multi-scheduling has been blocked, only
one scheduler thread will schedule Erlang processes.

If BlockState =:= block, multi-scheduling will
be blocked. If BlockState =:= unblock and no-one
else is blocking multi-scheduling and this process has
only blocked one time, multi-scheduling will be unblocked.
One process can block multi-scheduling multiple times.
If a process has blocked multiple times, it has to
unblock exactly as many times as it has blocked before it
has released its multi-scheduling block. If a process that
has blocked multi-scheduling exits, it will release its
blocking of multi-scheduling.

The return values are disabled, blocked,
or enabled. The returned value describes the
state just after the call to
erlang:system_flag(multi_scheduling, BlockState)
has been made. The return values are described in the
documentation of erlang:system_info(multi_scheduling).

NOTE: Blocking of multi-scheduling should normally
not be needed. If you feel that you need to
block multi-scheduling, think through the
problem at least a couple of times again.
Blocking multi-scheduling should only be used
as a last resort since it will most likely be
a very inefficient way to solve the
problem.

This argument is deprecated and
scheduled for removal in erts-5.10/OTP-R16. Instead of using
this argument you are advised to use the erl command
line argument +sbt.
When this argument has been removed a final scheduler bind type
to use will be determined at emulator boot time.

Controls if and how schedulers are bound to logical
processors.

When erlang:system_flag(scheduler_bind_type, How) is
called, an asynchronous signal is sent to all schedulers
online which causes them to try to bind or unbind as requested.
NOTE: If a scheduler fails to bind, this
will often be silently ignored. This since it isn't always
possible to verify valid logical processor identifiers. If
an error is reported, it will be reported to the
error_logger. If you want to verify that the
schedulers actually have bound as requested, call
erlang:system_info(scheduler_bindings).

Schedulers can currently only be bound on newer Linux,
Solaris, FreeBSD, and Windows systems, but more systems will be
supported in the future.

In order for the runtime system to be able to bind schedulers,
the CPU topology needs to be known. If the runtime system fails
to automatically detect the CPU topology, it can be defined.
For more information on how to define the CPU topology, see
the erl+sct command
line flag.

The runtime system will by default not bind schedulers
to logical processors.

NOTE: If the Erlang runtime system is the only
operating system process that binds threads to logical processors,
this improves the performance of the runtime system. However,
if other operating system processes (as for example another Erlang
runtime system) also bind threads to logical processors, there
might be a performance penalty instead. In some cases this
performance penalty might be severe. If this is the case, you
are advised to not bind the schedulers.

Schedulers can be bound in different ways. The How
argument determines how schedulers are bound. How can
currently be one of:

Sets the value of the node's trace control word to
TCW. TCW should be an unsigned integer. For
more information see documentation of the
set_tcw
function in the match specification documentation in the
ERTS User's Guide.

Returns a list of tuples with information about
miscellaneous allocated memory areas.

Each tuple contains an atom describing type of memory as
first element and amount of allocated memory in bytes as
second element. In those cases when there is information
present about allocated and used memory, a third element
is present. This third element contains the amount of
used memory in bytes.

erlang:system_info(allocated_areas) is intended
for debugging, and the content is highly implementation
dependent. The content of the results will therefore
change when needed without prior notice.

Note: The sum of these values is not
the total amount of memory allocated by the emulator.
Some values are part of other values, and some memory
areas are not part of the result. If you are interested
in the total amount of memory allocated by the emulator
see erlang:memory/0,1.

Allocator corresponds to the malloc()
implementation used. If Allocator equals
undefined, the malloc() implementation
used could not be identified. Currently
glibc can be identified.

Version is a list of integers (but not a
string) representing the version of
the malloc() implementation used.

Features is a list of atoms representing
allocation features used.

Settings is a list of subsystems, their
configurable parameters, and used values. Settings
may differ between different combinations of
platforms, allocators, and allocation features.
Memory sizes are given in bytes.

Returns information about the specified allocator.
As of erts version 5.6.1 the return value is a list
of {instance, InstanceNo, InstanceInfo} tuples
where InstanceInfo contains information about
a specific instance of the allocator.
If Alloc is not a recognized allocator,
undefined is returned. If Alloc is disabled,
false is returned.

Note: The information returned is highly
implementation dependent and may be changed, or removed
at any time without prior notice. It was initially
intended as a tool when developing new allocators, but
since it might be of interest for others it has been
briefly documented.

The recognized allocators are listed in
erts_alloc(3).
After reading the erts_alloc(3) documentation,
the returned information
should more or less speak for itself. But it can be worth
explaining some things. Call counts are presented by two
values. The first value is giga calls, and the second
value is calls. mbcs, and sbcs are
abbreviations for, respectively, multi-block carriers, and
single-block carriers. Sizes are presented in bytes. When
it is not a size that is presented, it is the amount of
something. Sizes and amounts are often presented by three
values, the first is current value, the second is maximum
value since the last call to
erlang:system_info({allocator, Alloc}), and
the third is maximum value since the emulator was started.
If only one value is present, it is the current value.
fix_alloc memory block types are presented by two
values. The first value is memory pool size and
the second value used memory size.

Returns various information about the
CPU topology
of the current system
(emulator) as specified by Item:

cpu_topology

Returns the CpuTopology which currently is used by the
emulator. The CPU topology is used when binding schedulers
to logical processors. The CPU topology used is the
user
defined CPU topology if such exists; otherwise, the
automatically
detected CPU topology if such exists. If no CPU topology
exists, undefined is returned.

A level in the CpuTopology term can be omitted if
only one entry exists and the InfoList is empty.

thread can only be a sub level to core.
core can be a sub level to either processor
or node. processor can either be on the
top level or a sub level to node. node
can either be on the top level or a sub level to
processor. That is, NUMA nodes can be processor
internal or processor external. A CPU topology can
consist of a mix of processor internal and external
NUMA nodes, as long as each logical CPU belongs to one
and only one NUMA node. Cache hierarchy is not part of
the CpuTopology type yet, but will be in the
future. Other things may also make it into the CPU
topology in the future. In other words, expect the
CpuTopology type to change.

Returns the automatically detected CpuTopology. The
emulator currently only detects the CPU topology on some newer
Linux, Solaris, FreeBSD, and Windows systems. On Windows system with
more than 32 logical processors the CPU topology is not detected.

For more information see the documentation of the
cpu_topology
argument.

{cpu_topology, used}

Returns the CpuTopology which is used by the
emulator. For more information see the
documentation of the
cpu_topology
argument.

Returns an atom describing the build type of the runtime
system. This is normally the atom opt for optimized.
Other possible return values are debug, purify,
quantify, purecov, gcov, valgrind,
gprof, and lcnt. Possible return values
may be added and/or removed at any time without prior notice.

c_compiler_used

Returns a two-tuple describing the C compiler used when
compiling the runtime system. The first element is an
atom describing the name of the compiler, or undefined
if unknown. The second element is a term describing the
version of the compiler, or undefined if unknown.

check_io

Returns a list containing miscellaneous information
regarding the emulators internal I/O checking. Note,
the content of the returned list may vary between
platforms and over time. The only thing guaranteed is
that a list is returned.

compat_rel

Returns the compatibility mode of the local node as
an integer. The integer returned represents the
Erlang/OTP release which the current emulator has been
set to be backward compatible with. The compatibility
mode can be configured at startup by using the command
line flag +R, see
erl(1).

Returns the creation of the local node as an integer.
The creation is changed when a node is restarted. The
creation of a node is stored in process identifiers, port
identifiers, and references. This makes it (to some
extent) possible to distinguish between identifiers from
different incarnations of a node. Currently valid
creations are integers in the range 1..3, but this may
(probably will) change in the future. If the node is not
alive, 0 is returned.

debug_compiled

Returns true if the emulator has been debug
compiled; otherwise, false.

dist

Returns a binary containing a string of distribution
information formatted as in Erlang crash dumps. For more
information see the "How to interpret the Erlang crash dumps"
chapter in the ERTS User's Guide.

dist_ctrl

Returns a list of tuples
{Node, ControllingEntity}, one entry for each
connected remote node. The Node is the name of the
node and the ControllingEntity is the port or pid
responsible for the communication to that node. More
specifically, the ControllingEntity for nodes
connected via TCP/IP (the normal case) is the socket
actually used in communication with the specific node.

driver_version

Returns a string containing the erlang driver version
used by the runtime system. It will be on the form
"<major ver>.<minor ver>".

dynamic_trace

Returns an atom describing the dynamic trace framework
compiled into the virtual machine. It can currently be either
dtrace, systemtap or none. For a
commercial or standard build, this is always none,
the other return values indicate a custom configuration
(e.g. ./configure --with-dynamic-trace=dtrace). See
the dyntrace
manual page and the
README.dtrace/README.systemtap files in the
Erlang source code top directory for more information
about dynamic tracing.

dynamic_trace_probes

Returns a boolean() indicating if dynamic trace probes
(either dtrace or systemtap) are built into the
emulator. This can only be true if the virtual
machine was built for dynamic tracing
(i.e. system_info(dynamic_trace) returns
dtrace or systemtap).

elib_malloc

This option will be removed in a future release.
The return value will always be false since
the elib_malloc allocator has been removed.

Returns the value of the distribution buffer busy limit
in bytes. This limit can be set on startup by passing the
+zdbbl command line
flag to erl.

fullsweep_after

Returns {fullsweep_after, integer() >= 0} which is the
fullsweep_after garbage collection setting used
by default. For more information see
garbage_collection described below.

garbage_collection

Returns a list describing the default garbage collection
settings. A process spawned on the local node by a
spawn or spawn_link will use these
garbage collection settings. The default settings can be
changed by use of
system_flag/2.
spawn_opt/4
can spawn a process that does not use the default
settings.

heap_sizes

Returns a list of integers representing valid heap sizes
in words. All Erlang heaps are sized from sizes in this
list.

heap_type

Returns the heap type used by the current emulator.
Currently only the following heap type exists:

private

Each process has a heap reserved for its use and no
references between heaps of different processes are
allowed. Messages passed between processes are copied
between heaps.

info

Returns a binary containing a string of miscellaneous
system information formatted as in Erlang crash dumps.
For more information see the
"How to interpret the Erlang crash dumps" chapter in the ERTS
User's Guide.

kernel_poll

Returns true if the emulator uses some kind of
kernel-poll implementation; otherwise, false.

loaded

Returns a binary containing a string of loaded module
information formatted as in Erlang crash dumps. For more
information see the "How to interpret the Erlang crash dumps" chapter
in the ERTS User's Guide.

Returns the detected number of logical processors configured
on the system. The return value is either an integer, or
the atom unknown if the emulator wasn't able to
detect logical processors configured.

Returns the detected number of logical processors available to
the Erlang runtime system. The return value is either an
integer, or the atom unknown if the emulator wasn't
able to detect logical processors available. The number
of logical processors available is less than or equal to
the number of logical
processors online.

Returns the detected number of logical processors online on
the system. The return value is either an integer,
or the atom unknown if the emulator wasn't able to
detect logical processors online. The number of logical
processors online is less than or equal to the number of
logical processors
configured.

machine

Returns a string containing the Erlang machine name.

min_heap_size

Returns {min_heap_size, MinHeapSize} where MinHeapSize is the current system wide
minimum heap size for spawned processes.

min_bin_vheap_size

Returns {min_bin_vheap_size, MinBinVHeapSize} where MinBinVHeapSize is the current system wide
minimum binary virtual heap size for spawned processes.

modified_timing_level

Returns the modified timing level (an integer) if
modified timing has been enabled; otherwise,
undefined. See the +T command line flag
in the documentation of the
erl(1)
command for more information on modified timing.

Returns a list of PIDs when multi-scheduling
is blocked; otherwise, the empty list. The PIDs
in the list is PIDs of the processes currently
blocking multi-scheduling. A PID will only be
present once in the list, even if the corresponding
process has blocked multiple times.

Returns the maximum number of simultaneously existing
processes at the local node as an integer. This limit
can be configured at startup by using the
+P
command line flag of
erl(1).

procs

Returns a binary containing a string of process and port
information formatted as in Erlang crash dumps. For more
information see the "How to interpret the Erlang crash dumps" chapter
in the ERTS User's Guide.

A tuple of a size equal to
erlang:system_info(schedulers) is returned. The elements of the tuple are integers
or the atom unbound. Logical processor identifiers
are represented as integers. The Nth
element of the tuple equals the current binding for
the scheduler with the scheduler identifier equal to
N. E.g., if the schedulers have been bound,
element(erlang:system_info(scheduler_id),
erlang:system_info(scheduler_bindings)) will return
the identifier of the logical processor that the calling
process is executing on.

Returns the scheduler id (SchedulerId) of the
scheduler thread that the calling process is executing
on. SchedulerId is a positive integer; where
1 <= SchedulerId <= erlang:system_info(schedulers). See also
erlang:system_info(schedulers).

Returns the size of Erlang term words in bytes as an
integer, i.e. on a 32-bit architecture 4 is returned,
and on a pure 64-bit architecture 8 is returned. On a
halfword 64-bit emulator, 4 is returned, as the Erlang
terms are stored using a virtual wordsize of half the
system's wordsize.

{wordsize, external}

Returns the true wordsize of the emulator, i.e. the size
of a pointer, in bytes as an integer. On a pure 32-bit
architecture 4 is returned, on both a halfword and pure
64-bit architecture, 8 is returned.

Note

The scheduler argument has changed name to
scheduler_id. This in order to avoid mixup with
the schedulers argument. The scheduler
argument was introduced in ERTS version 5.5 and renamed
in ERTS version 5.5.1.

Returns the current system monitoring settings set by
erlang:system_monitor/2
as {MonitorPid, Options}, or undefined if there
are no settings. The order of the options may be different
from the one that was set.

Sets system performance monitoring options. MonitorPid
is a local pid that will receive system monitor messages, and
the second argument is a list of monitoring options:

{long_gc, Time}

If a garbage collection in the system takes at least
Time wallclock milliseconds, a message
{monitor, GcPid, long_gc, Info} is sent to
MonitorPid. GcPid is the pid that was
garbage collected and Info is a list of two-element
tuples describing the result of the garbage collection.
One of the tuples is {timeout, GcTime} where
GcTime is the actual time for the garbage
collection in milliseconds. The other tuples are
tagged with heap_size, heap_block_size,
stack_size, mbuf_size, old_heap_size,
and old_heap_block_size. These tuples are
explained in the documentation of the
gc_start
trace message (see
erlang:trace/3).
New tuples may be added, and the order of the tuples in
the Info list may be changed at any time without prior
notice.

{long_schedule, Time}

If a process or port in the system runs uninterrupted
for at least Time wall clock milliseconds, a
message {monitor, PidOrPort, long_schedule, Info}
is sent to MonitorPid. PidOrPort is the
process or port that was running and Info is a
list of two-element tuples describing the event. In case
of a pid(), the tuples {timeout, Millis},
{in, Location} and {out, Location} will be
present, where Location is either an MFA
({Module, Function, Arity}) describing the
function where the process was scheduled in/out, or the
atom undefined. In case of a port(), the
tuples {timeout, Millis} and {port_op,Op}
will be present. Op will be one of proc_sig,
timeout, input, output,
event or dist_cmd, depending on which
driver callback was executing. proc_sig is an
internal operation and should never appear, while the
others represent the corresponding driver callbacks
timeout, ready_input, ready_output,
event and finally outputv (when the port
is used by distribution). The Millis value in
the timeout tuple will tell you the actual
uninterrupted execution time of the process or port,
which will always be >= the Time value
supplied when starting the trace. New tuples may be
added to the Info list in the future, and the
order of the tuples in the list may be changed at any
time without prior notice.

This can be used to detect problems with NIF's or
drivers that take too long to execute. Generally, 1 ms
is considered a good maximum time for a driver callback
or a NIF. However, a time sharing system should usually
consider everything below 100 ms as "possible" and
fairly "normal". Schedule times above that might however
indicate swapping or a NIF/driver that is
misbehaving. Misbehaving NIF's and drivers could cause
bad resource utilization and bad overall performance of
the system.

{large_heap, Size}

If a garbage collection in the system results in
the allocated size of a heap being at least Size
words, a message {monitor, GcPid, large_heap, Info}
is sent to MonitorPid. GcPid and Info
are the same as for long_gc above, except that
the tuple tagged with timeout is not present.
Note: As of erts version 5.6 the monitor message
is sent if the sum of the sizes of all memory blocks allocated
for all heap generations is equal to or larger than Size.
Previously the monitor message was sent if the memory block
allocated for the youngest generation was equal to or larger
than Size.

busy_port

If a process in the system gets suspended because it
sends to a busy port, a message
{monitor, SusPid, busy_port, Port} is sent to
MonitorPid. SusPid is the pid that got
suspended when sending to Port.

busy_dist_port

If a process in the system gets suspended because it
sends to a process on a remote node whose inter-node
communication was handled by a busy port, a message
{monitor, SusPid, busy_dist_port, Port} is sent to
MonitorPid. SusPid is the pid that got
suspended when sending through the inter-node
communication port Port.

If a monitoring process gets so large that it itself
starts to cause system monitor messages when garbage
collecting, the messages will enlarge the process's
message queue and probably make the problem worse.

Keep the monitoring process neat and do not set the system
monitor limits too tight.

Failure: badarg if MonitorPid does not exist or is not a local process.

Returns the current system profiling settings set by
erlang:system_profile/2
as {ProfilerPid, Options}, or undefined if there
are no settings. The order of the options may be different
from the one that was set.

Sets system profiler options. ProfilerPid
is a local pid or port that will receive profiling messages. The
receiver is excluded from all profiling.
The second argument is a list of profiling options:

exclusive

If a synchronous call to a port from a process is done, the
calling process is considered not runnable during the call
runtime to the port. The calling process is notified as
inactive and subsequently active when the port
callback returns.

runnable_procs

If a process is put into or removed from the run queue a message,
{profile, Pid, State, Mfa, Ts}, is sent to
ProfilerPid. Running processes that is reinserted into the
run queue after having been preemptively scheduled out will not trigger this
message.

runnable_ports

If a port is put into or removed from the run queue a message,
{profile, Port, State, 0, Ts}, is sent to
ProfilerPid.

scheduler

If a scheduler is put to sleep or awoken a message,
{profile, scheduler, Id, State, NoScheds, Ts}, is sent
to ProfilerPid.

Note

erlang:system_profile is considered experimental and
its behaviour may change in the future.

Returns a binary data object which is the result of encoding
Term according to the Erlang external term format.

This can be used for a variety of purposes, for example
writing a term to a file in an efficient way, or sending an
Erlang term to some type of communications channel not
supported by distributed Erlang.

Returns a binary data object which is the result of encoding
Term according to the Erlang external term format.

If the option compressed is provided, the external
term format will be compressed. The compressed format is
automatically recognized by binary_to_term/1 in R7B and later.

It is also possible to specify a compression level by giving
the option {compressed, Level}, where Level is an
integer from 0 through 9. 0 means that no compression
will be done (it is the same as not giving any compressed option);
1 will take the least time but may not compress as well as
the higher levels; 9 will take the most time and may produce
a smaller result. Note the "mays" in the preceding sentence; depending
on the input term, level 9 compression may or may not produce a smaller
result than level 1 compression.

Currently, compressed gives the same result as
{compressed, 6}.

The option {minor_version, Version} can be use to control
some details of the encoding. This option was
introduced in R11B-4. Currently, the allowed values for Version
are 0 and 1.

{minor_version, 1} forces any floats in the term to be encoded
in a more space-efficient and exact way (namely in the 64-bit IEEE format,
rather than converted to a textual representation). binary_to_term/1
in R11B-4 and later is able decode the new representation.

{minor_version, 0} is currently the default, meaning that floats
will be encoded using a textual representation; this option is useful if
you want to ensure that releases prior to R11B-4 can decode resulting
binary.

Used in conjunction with the call trace flag.
The call, return_from and return_to
trace messages are inhibited if this flag is set,
but if there are match specs they are executed as normal.

Silent mode is inhibited by executing
erlang:trace(_, false, [silent|_]),
or by a match spec executing the {silent, false}
function.

The silent trace flag facilitates setting up
a trace on many or even all processes in the system.
Then the interesting trace can be activated and
deactivated using the {silent,Bool}
match spec function, giving a high degree
of control of which functions with which
arguments that triggers the trace.

Used in conjunction with the call trace flag.
Trace the actual return from a traced function back to
its caller. Only works for functions traced with
the local option to
erlang:trace_pattern/3.

The semantics is that a trace message is sent when a
call traced function actually returns, that is, when a
chain of tail recursive calls is ended. There will be
only one trace message sent per chain of tail recursive
calls, why the properties of tail recursiveness for
function calls are kept while tracing with this flag.
Using call and return_to trace together
makes it possible to know exactly in which function a
process executes at any time.

To get trace messages containing return values from
functions, use the {return_trace} match_spec
action instead.

Message tags: return_to.

running

Trace scheduling of processes.

Message tags: in, and out.

exiting

Trace scheduling of an exiting processes.

Message tags: in_exiting, out_exiting, and
out_exited.

garbage_collection

Trace garbage collections of processes.

Message tags: gc_start, gc_end.

timestamp

Include a time stamp in all trace messages. The time
stamp (Ts) is of the same form as returned by
erlang:now().

cpu_timestamp

A global trace flag for the Erlang node that makes all
trace timestamps be in CPU time, not wallclock. It is
only allowed with PidSpec==all. If the host
machine operating system does not support high resolution
CPU time measurements, trace/3 exits with
badarg.

arity

Used in conjunction with the call trace flag.
{M, F, Arity} will be specified instead of
{M, F, Args} in call trace messages.

set_on_spawn

Makes any process created by a traced process inherit
its trace flags, including the set_on_spawn flag.

set_on_first_spawn

Makes the first process created by a traced process
inherit its trace flags, excluding
the set_on_first_spawn flag.

set_on_link

Makes any process linked by a traced process inherit its
trace flags, including the set_on_link flag.

set_on_first_link

Makes the first process linked to by a traced process
inherit its trace flags, excluding
the set_on_first_link flag.

{tracer, Tracer}

Specify where to send the trace messages. Tracer
must be the pid of a local process or the port identifier
of a local port. If this flag is not given, trace
messages will be sent to the process that called
erlang:trace/3.

The effect of combining set_on_first_link with
set_on_link is the same as having
set_on_first_link alone. Likewise for
set_on_spawn and set_on_first_spawn.

If the timestamp flag is not given, the tracing
process will receive the trace messages described below.
Pid is the pid of the traced process in which
the traced event has occurred. The third element of the tuple
is the message tag.

If the timestamp flag is given, the first element of
the tuple will be trace_ts instead and the timestamp
is added last in the tuple.

{trace, Pid, 'receive', Msg}

When Pid receives the message Msg.

{trace, Pid, send, Msg, To}

When Pid sends the message Msg to
the process To.

{trace, Pid, send_to_non_existing_process, Msg, To}

When Pid sends the message Msg to
the non-existing process To.

{trace, Pid, call, {M, F, Args}}

When Pid calls a traced function. The return
values of calls are never supplied, only the call and its
arguments.

Note that the trace flag arity can be used to
change the contents of this message, so that Arity
is specified instead of Args.

{trace, Pid, return_to, {M, F, Arity}}

When Pid returns to the specified
function. This trace message is sent if both
the call and the return_to flags are set,
and the function is set to be traced on local
function calls. The message is only sent when returning
from a chain of tail recursive function calls where at
least one call generated a call trace message
(that is, the functions match specification matched and
{message, false} was not an action).

{trace, Pid, return_from, {M, F, Arity}, ReturnValue}

When Pid returns from the specified
function. This trace message is sent if the call
flag is set, and the function has a match specification
with a return_trace or exception_trace action.

{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}

When Pid exits from the specified
function due to an exception. This trace message is sent
if the call flag is set, and the function has
a match specification with an exception_trace action.

{trace, Pid, spawn, Pid2, {M, F, Args}}

When Pid spawns a new process Pid2 with
the specified function call as entry point.

Note that Args is supposed to be the argument
list, but may be any term in the case of an erroneous
spawn.

{trace, Pid, exit, Reason}

When Pid exits with reason Reason.

{trace, Pid, link, Pid2}

When Pid links to a process Pid2.

{trace, Pid, unlink, Pid2}

When Pid removes the link from a process
Pid2.

{trace, Pid, getting_linked, Pid2}

When Pid gets linked to a process Pid2.

{trace, Pid, getting_unlinked, Pid2}

When Pid gets unlinked from a process Pid2.

{trace, Pid, register, RegName}

When Pid gets the name RegName registered.

{trace, Pid, unregister, RegName}

When Pid gets the name RegName unregistered.
Note that this is done automatically when a registered
process exits.

{trace, Pid, in, {M, F, Arity} | 0}

When Pid is scheduled to run. The process will
run in function {M, F, Arity}. On some rare
occasions the current function cannot be determined, then
the last element Arity is 0.

{trace, Pid, out, {M, F, Arity} | 0}

When Pid is scheduled out. The process was
running in function {M, F, Arity}. On some rare occasions
the current function cannot be determined, then the last
element Arity is 0.

Sent when garbage collection is about to be started.
Info is a list of two-element tuples, where
the first element is a key, and the second is the value.
You should not depend on the tuples have any defined
order. Currently, the following keys are defined:

heap_size

The size of the used part of the heap.

heap_block_size

The size of the memory block used for storing
the heap and the stack.

old_heap_size

The size of the used part of the old heap.

old_heap_block_size

The size of the memory block used for storing
the old heap.

stack_size

The actual size of the stack.

recent_size

The size of the data that survived the previous garbage
collection.

mbuf_size

The combined size of message buffers associated with
the process.

bin_vheap_size

The total size of unique off-heap binaries referenced from the process heap.

bin_vheap_block_size

The total size of binaries, in words, allowed in the virtual
heap in the process before doing a garbage collection.

bin_old_vheap_size

The total size of unique off-heap binaries referenced from the process old heap.

bin_vheap_block_size

The total size of binaries, in words, allowed in the virtual
old heap in the process before doing a garbage collection.

All sizes are in words.

{trace, Pid, gc_end, Info}

Sent when garbage collection is finished. Info
contains the same kind of list as in the gc_start
message, but the sizes reflect the new sizes after
garbage collection.

If the tracing process dies, the flags will be silently
removed.

Only one process can trace a particular process. For this
reason, attempts to trace an already traced process will fail.

Returns: A number indicating the number of processes that
matched PidSpec. If PidSpec is a pid,
the return value will be 1. If PidSpec is
all or existing the return value will be
the number of processes running, excluding tracer processes.
If PidSpec is new, the return value will be
0.

Failure: If specified arguments are not supported. For
example cpu_timestamp is not supported on all
platforms.

erlang:trace_delivered(Tracee) -> Ref

Types:

Tracee = pid() | all

Ref = reference()

The delivery of trace messages is dislocated on the time-line
compared to other events in the system. If you know that the
Tracee has passed some specific point in its execution,
and you want to know when at least all trace messages
corresponding to events up to this point have reached the tracer
you can use erlang:trace_delivered(Tracee). A
{trace_delivered, Tracee, Ref} message is sent to
the caller of erlang:trace_delivered(Tracee) when it
is guaranteed that all trace messages have been delivered to
the tracer up to the point that the Tracee had reached
at the time of the call to
erlang:trace_delivered(Tracee).

Note that the trace_delivered message does not
imply that trace messages have been delivered; instead, it implies
that all trace messages that should be delivered have
been delivered. It is not an error if Tracee isn't, and
hasn't been traced by someone, but if this is the case,
no trace messages will have been delivered when the
trace_delivered message arrives.

Note that Tracee has to refer to a process currently,
or previously existing on the same node as the caller of
erlang:trace_delivered(Tracee) resides on.
The special Tracee atom all denotes all processes
that currently are traced in the node.

An example: Process A is Tracee, port B is
tracer, and process C is the port owner of B.
C wants to close B when A exits. C
can ensure that the trace isn't truncated by calling
erlang:trace_delivered(A) when A exits and wait
for the {trace_delivered, A, Ref} message before closing
B.

Failure: badarg if Tracee does not refer to a
process (dead or alive) on the same node as the caller of
erlang:trace_delivered(Tracee) resides on.

To get information about a process, PidOrFunc should
be a pid or the atom new. The atom new means
that the default trace state for processes to be created will
be returned. Item must have one of the following
values:

flags

Return a list of atoms indicating what kind of traces is
enabled for the process. The list will be empty if no
traces are enabled, and one or more of the followings
atoms if traces are enabled: send,
'receive', set_on_spawn, call,
return_to, procs, set_on_first_spawn,
set_on_link, running,
garbage_collection, timestamp, and
arity. The order is arbitrary.

tracer

Return the identifier for process or port tracing this
process. If this process is not being traced, the return
value will be [].

To get information about a function, PidOrFunc should
be a three-element tuple: {Module, Function, Arity} or
the atom on_load. No wildcards are allowed. Returns
undefined if the function does not exist or
false if the function is not traced at all. Item
must have one of the following values:

traced

Return global if this function is traced on
global function calls, local if this function is
traced on local function calls (i.e local and global
function calls), and false if neither local nor
global function calls are traced.

match_spec

Return the match specification for this function, if it
has one. If the function is locally or globally traced but
has no match specification defined, the returned value
is [].

meta

Return the meta trace tracer process or port for this
function, if it has one. If the function is not meta
traced the returned value is false, and if
the function is meta traced but has once detected that
the tracer proc is invalid, the returned value is [].

meta_match_spec

Return the meta trace match specification for this
function, if it has one. If the function is meta traced
but has no match specification defined, the returned
value is [].

call_count

Return the call count value for this function or
true for the pseudo function on_load if call
count tracing is active. Return false otherwise.
See also
erlang:trace_pattern/3.

call_time

Return the call time values for this function or
true for the pseudo function on_load if call
time tracing is active. Returns false otherwise.
The call time values returned, [{Pid, Count, S, Us}],
is a list of each process that has executed the function and its specific counters.
See also
erlang:trace_pattern/3.

all

Return a list containing the {Item, Value} tuples
for all other items, or return false if no tracing
is active for this function.

The actual return value will be {Item, Value}, where
Value is the requested information as described above.
If a pid for a dead process was given, or the name of a
non-existing function, Value will be undefined.

If PidOrFunc is the on_load, the information
returned refers to the default value for code that will be
loaded.

This BIF is used to enable or disable call tracing for
exported functions. It must be combined with
erlang:trace/3
to set the call trace flag for one or more processes.

Conceptually, call tracing works like this: Inside
the Erlang virtual machine there is a set of processes to be
traced and a set of functions to be traced. Tracing will be
enabled on the intersection of the set. That is, if a process
included in the traced process set calls a function included
in the traced function set, the trace action will be taken.
Otherwise, nothing will happen.

Use
erlang:trace/3 to
add or remove one or more processes to the set of traced
processes. Use erlang:trace_pattern/2 to add or remove
exported functions to the set of traced functions.

The erlang:trace_pattern/3 BIF can also add match
specifications to an exported function. A match specification
comprises a pattern that the arguments to the function must
match, a guard expression which must evaluate to true
and an action to be performed. The default action is to send a
trace message. If the pattern does not match or the guard
fails, the action will not be executed.

The MFA argument should be a tuple like
{Module, Function, Arity} or the atom on_load
(described below). It can be the module, function, and arity
for an exported function (or a BIF in any module).
The '_' atom can be used to mean any of that kind.
Wildcards can be used in any of the following ways:

{Module,Function,'_'}

All exported functions of any arity named Function
in module Module.

{Module,'_','_'}

All exported functions in module Module.

{'_','_','_'}

All exported functions in all loaded modules.

Other combinations, such as {Module,'_',Arity}, are
not allowed. Local functions will match wildcards only if
the local option is in the FlagList.

If the MFA argument is the atom on_load,
the match specification and flag list will be used on all
modules that are newly loaded.

The MatchSpec argument can take any of the following
forms:

false

Disable tracing for the matching function(s). Any match
specification will be removed.

true

Enable tracing for the matching function(s).

MatchSpecList

A list of match specifications. An empty list is
equivalent to true. See the ERTS User's Guide
for a description of match specifications.

restart

For the FlagList option call_count and call_time:
restart the existing counters. The behaviour is undefined
for other FlagList options.

pause

For the FlagList option call_count and call_time: pause
the existing counters. The behaviour is undefined for
other FlagList options.

The FlagList parameter is a list of options.
The following options are allowed:

global

Turn on or off call tracing for global function calls
(that is, calls specifying the module explicitly). Only
exported functions will match and only global calls will
generate trace messages. This is the default.

local

Turn on or off call tracing for all types of function
calls. Trace messages will be sent whenever any of
the specified functions are called, regardless of how they
are called. If the return_to flag is set for
the process, a return_to message will also be sent
when this function returns to its caller.

meta | {meta, Pid}

Turn on or off meta tracing for all types of function
calls. Trace messages will be sent to the tracer process
or port Pid whenever any of the specified
functions are called, regardless of how they are called.
If no Pid is specified, self() is used as a
default tracer process.

Meta tracing traces all processes and does not care
about the process trace flags set by trace/3,
the trace flags are instead fixed to
[call, timestamp].

The match spec function {return_trace} works with
meta trace and send its trace message to the same tracer
process.

call_count

Starts (MatchSpec == true) or stops
(MatchSpec == false) call count tracing for all
types of function calls. For every function a counter is
incremented when the function is called, in any process.
No process trace flags need to be activated.

If call count tracing is started while already running,
the count is restarted from zero. Running counters can be
paused with MatchSpec == pause. Paused and running
counters can be restarted from zero with
MatchSpec == restart.

Starts (MatchSpec == true) or stops
(MatchSpec == false) call time tracing for all
types of function calls. For every function a counter is
incremented when the function is called. Time spent in the function
is accumulated in two other counters, seconds and micro-seconds.
The counters are stored for each call traced process.

If call time tracing is started while already running,
the count and time is restarted from zero. Running counters can be
paused with MatchSpec == pause. Paused and running
counters can be restarted from zero with
MatchSpec == restart.

The global and local options are mutually
exclusive and global is the default (if no options are
specified). The call_count and meta options
perform a kind of local tracing, and can also not be combined
with global. A function can be either globally or
locally traced. If global tracing is specified for a
specified set of functions; local, meta, call time and call count
tracing for the matching set of local functions will be
disabled, and vice versa.

When disabling trace, the option must match the type of trace
that is set on the function, so that local tracing must be
disabled with the local option and global tracing with
the global option (or no option at all), and so forth.

There is no way to directly change part of a match
specification list. If a function has a match specification,
you can replace it with a completely new one. If you need to
change an existing match specification, use the
erlang:trace_info/2
BIF to retrieve the existing match specification.

Returns the number of exported functions that matched
the MFA argument. This will be zero if none matched at
all.

trunc(Number) -> integer()

Types:

Number = number()

Returns an integer by the truncating Number.

> trunc(5.5).
5

Allowed in guard tests.

tuple_size(Tuple) -> integer() >= 0

Types:

Tuple = tuple()

Returns an integer which is the number of elements in Tuple.

> tuple_size({morni, mulle, bwange}).
3

Allowed in guard tests.

tuple_to_list(Tuple) -> [term()]

Types:

Tuple = tuple()

Returns a list which corresponds to Tuple.
Tuple may contain any Erlang terms.

Returns the current date and time according to Universal
Time Coordinated (UTC), also called GMT, in the form
{{Year, Month, Day}, {Hour, Minute, Second}} if
supported by the underlying operating system. If not,
erlang:universaltime() is equivalent to
erlang:localtime().

Failure: badarg if Universaltime does not denote
a valid date and time.

unlink(Id) -> true

Types:

Id = pid() | port()

Removes the link, if there is one, between the calling
process and the process or port referred to by Id.

Returns true and does not fail, even if there is no
link to Id, or if Id does not exist.

Once unlink(Id) has returned it is guaranteed that
the link between the caller and the entity referred to by
Id has no effect on the caller in the future (unless
the link is setup again). If caller is trapping exits, an
{'EXIT', Id, _} message due to the link might have
been placed in the caller's message queue prior to the call,
though. Note, the {'EXIT', Id, _} message can be the
result of the link, but can also be the result of Id
calling exit/2. Therefore, it may be
appropriate to cleanup the message queue when trapping exits
after the call to unlink(Id), as follow:

unlink(Id),
receive
{'EXIT', Id, _} ->
true
after 0 ->
true
end

Note

Prior to OTP release R11B (erts version 5.5) unlink/1
behaved completely asynchronous, i.e., the link was active
until the "unlink signal" reached the linked entity. This
had one undesirable effect, though. You could never know when
you were guaranteed not to be effected by the link.

Current behavior can be viewed as two combined operations:
asynchronously send an "unlink signal" to the linked entity
and ignore any future results of the link.

unregister(RegName) -> true

Types:

RegName = atom()

Removes the registered name RegName, associated with a
pid or a port identifier.

> unregister(db).
true

Users are advised not to unregister system processes.

Failure: badarg if RegName is not a registered
name.

whereis(RegName) -> pid() | port() | undefined

Types:

RegName = atom()

Returns the pid or port identifier with the registered name
RegName. Returns undefined if the name is not
registered.

> whereis(db).
<0.43.0>

erlang:yield() -> true

Voluntarily let other processes (if any) get a chance to
execute. Using erlang:yield() is similar to
receive after 1 -> ok end, except that yield()
is faster.

Warning

There is seldom or never any need to use this BIF,
especially in the SMP-emulator as other processes will have a
chance to run in another scheduler thread anyway.
Using this BIF without a thorough grasp of how the scheduler
works may cause performance degradation.